key: cord-0059734-t8w9i8dd
authors: Bickl, Thomas
title: The Four Development Phases of the Croatia-Slovenia Border Dispute
date: 2020-10-02
journal: The Border Dispute Between Croatia and Slovenia
DOI: 10.1007/978-3-030-53333-5_4
sha: d2f810158bfdeed0a64b8a77e9c2dc17609c8c79
doc_id: 59734
cord_uid: t8w9i8dd

The current Chapter is at the heart of attempts to resolve the Croatian-Slovenian border dispute. The aim is to trace the processes in the resolution efforts with regard to issues, actors, and conflict dynamics. The management process of the border dispute is grouped into four stages: (i) the bilateral phase (1992–2007) when both countries were negotiating with each other, but were unable to produce a binding settlement, although a bilateral treaty had been successfully negotiated at the highest political level in 2001; (ii) Croatia’s EU accession negotiations (2008/2009) when the dispute triggered a veto by Slovenia and subsequently involved third parties in the form of the European Commission and the EU Council Presidency; (iii) the arbitral proceedings (2012–2017)—the result of externalising the resolution of the substantive dispute to third-party judicial dispute resolution—which imploded due to illegal communication and yet produced a binding settlement under international law; and (iv) the infringement proceedings against Croatia brought before the EU Court of Justice by Slovenia on the grounds that the non-implementation of the Final Award by Croatia constituted a breach of the territorial application of EU law, a plea for which the Court found it had no jurisdiction (2018–2020). Interviewees include Miro Cerar, Alojz Peterle, Andrej Plenković, Vesna Pusić, Olli Rehn, and Ivo Sanader.

Croatia protested about the works on 21 June, four days before the joint independence declarations, 1 on the grounds that Slovenia was building the checkpoint on Croatian territory (see e.g. Ministry of Foreign Affairs Croatia press release, 12 May 2006) . After a few hours of telephone diplomacy, Slovenia withdrew its workers and started constructing a temporary Sečovlje checkpoint north of the Dragonja next to the Mlini hamlet instead (interview Alojz Peterle, 16-09-2015) . The reasoning behind that move was that an open conflict at the Slovenian-Croatian border may have been a pretext for the Yugoslav army (JNA) to step in (Ministry of Foreign Affairs Slovenia White Paper on the border between Slovenia and Croatia 2006: 23-24) . Ironically, Croatia later completed the works on what was originally a Slovenian checkpoint south of the river and made it the Croatian Plovanija checkpoint. Slovenia repeatedly protested about Croatia operating that crossing point south of the river (Ministry of Foreign Affairs Slovenia White Paper 2006: 26; see also Sect. 4.2.2.1 on the Slovenian blockade in October 2008, and Fig. 4.1) . Nevertheless, both checkpoints became permanent ones over time. 2 In the first two years after independence, the border with Slovenia played virtually no role in Croatia since the focus of attention to territorial issues was on the Homeland War 1991 in the Krajina, Northern Dalmatia, and in Eastern Slavonia (interview Vesna Pusić, 24-02-2017 interview Ivo Sanader, 19-05-2016 ; for the Homeland War see Sect. 2.5.2).

A number of joint bodies were set up in 1992 and 1993 on the political and technical level. On 30 July 1993, the Agreement on the Establishment of Joint Bodies for the Establishment and Identification/Demarcation of the State Border was signed which set up the Joint/Mixed Diplomatic Commission on the political level, and the Joint/Mixed Commission for Border Demarcation, Maintenance and Renewal at the technical level, the latter comprising several subsidiary Joint Expert Groups, such as the Group for the Comparison of the Cadastral Boundaries, the Group for Demarcation, and the Group for the Geodetic Basis (interview senior Slovenian civil servant, 17-10-2016; interview senior Croatian civil servant, 19-08-2016; see also PCA Partial Award 2016: 2, para 9; Sancin 2010: 96). A first technical-level bilateral meeting of surveying and mapping experts was held on 26 May 1992 where it was agreed that the definition of the cadastral boundaries would be the starting point for the delimitation of the land border. After another meeting on 15 March 1993 where an understanding was reached to identify diverging interpretations of the cadastral border, the final report of the surveying and mapping experts was adopted on 2 June 1994 (Crvtila 1993: 40; PCA Final Award 2017: 14-15, paras 51-56) . The report, based on 244 sheets of topographic maps at a scale of 1:50.000, noted that • 77%, i.e. approximately 510 km, of the common land border were aligned; • 10%, i.e. approximately 70 km, showed a mismatch of up to 2 cm on the maps; • 13%, i.e. 80 km of the joint border overlapped significantly (more than 2 cm) in the areas along the Mura and Drava river, at the confluence of the Sotla, Sava, and Bregana rivers, and in the following spots: along theČabranka river, at Snežnik, in the Topolec area, and along the lower reaches of the Dragonja between the Raven/Sečovlje municipalities on the Slovenian side and the Kaštel municipality on the Croatian side up to the mouth of the river (Joint Report 1994; cited in PCA Final Award 2017: 15-16, para 56).

The Expert Group report was fed into the Group for the Comparison of the Cadastral Boundaries (interview senior Slovenian civil servant, 17-10-2016).

The last official Expert Group Report was signed and issued on 20 December 1996 when there was talk of nine per cent or 60 km of the land boundary being unaligned in the sense of cadastral district boundaries diverging by more than 50 m on the ground (PCA Final Award 2017: 70, para 226) . In the Parties' submissions during the arbitration procedure starting in 2012, however, it emerged that Slovenia takes the view that the Report did not screen the cadastral records of the entire land border and that the Report was of a mere technical nature, whereas Croatia noted that the disputed areas were addressed and that this had indeed been the task of the Expert Group (PCA Final Award 2017: 21-22, paras 73-74) .

An early moment of dissenting views on the sea border emerged at a meeting of the joint expert group for establishing and marking the boundary on 16 March 1993 where Piran Bay (and the peak of Sveta Gera/Trdinov Vrh) became an issue. As for the sea border to be delimitated de novo, Slovenia favoured sovereignty over the entire Bay whilst Croatia opted for a partition of the Bay in terms of equal shares by way of the equidistance line (Cvrtila 1993: 41 ; see also PCA Final Award 2017: 71-72, paras 227-230; 76, paras 245-246) .

The Slovenian view soon became official through a Foreign Affairs Committee resolution of 7 April 1993 stating that, with regard to Piran Bay [t] he Republic of Slovenia advocated the maintenance of the integrity of the Bay of Piran under its sovereignty and jurisdiction and the exit to the high seas on the basis of admissible criteria of international law and taking into consideration the specific situation of the Republic of Slovenia.

The Republic of Slovenia holds a view that the Bay of Piran is a case sui generis which dictates exclusive regard of the historic title and other special circumstances. Slovenia, therefore, resolutely rejects the application of the criterion of the median line, which wouldin the case of the Bay of Piran -represent an unjust and impractical solution for the Republic of Slovenia, entirely contrary to the historical and actual state in the Bay of Piran. One should consider the fact that the Republic of Slovenia was executing jurisdiction and power over the Bay of Piran in the former SFRY and that such also was the existing state of affairs at the time of the proclamation of independence of both States […] on 25 June 1991. (Memorandum on the Bay of Piran, 7 April 1993: 3; emphasis added)

In respect of the maritime border in the territorial sea and access to the high seas, the Memorandum states:

From a Croatian point of view, the initial Slovenian law may be seen as an attempt to annex territory under de facto control 4 of Croatia. Conversely, a Slovenian viewpoint would underline the Slovenian claim 5 over the Three Hamlets to strengthen its bargaining position in the negotiations with Croatia (Klemenčić and Schofield 1995: 72 ; see also Pipan 2008: 342) .

As for the bilateral negotiations in the 1990s, the Joint Diplomatic Commission finished its work after the last unsuccessful meeting in July 1998. In 1999, the parties agreed to attempt third-party mediation seeking the good offices of William Perry, a former US Secretary of Defence. However, a joint meeting in Washington on 5 May 1999, and visits to Lubljana and Zagreb in June 1999 did not produce any results (interview senior Croatian civil servant, 19-08-2016; interview senior Slovenian civil servant, 17-10-2016; see also PCA Final Award 2017: 26, para 91). On balance, there was apparently little more common ground shared by the parties other than the mutual respect for the status quo on 25 June 1991 (Sancin 2010: 96) .

Despite the solidly protracted border conflict as such, Slovenia and Croatia successfully concluded a pragmatic accord on 25 April 1997, the Agreement on Local Border Traffic and Cooperation (SOPS). 6 It entered into force on 5 September 2001. SOPS is supposed to "improve living conditions of the population in the border areas" along the common border and to enable "free economic cooperation […] being aware that the border local communities are the foundations of good cooperation between Croatian administration, had Croatian ID cards, their Yugoslav passports were issued in Croatia, and the people from Škudelin, Bužin, and Škrilje who all have Croatian and Slovenian citizenship today were included in the census and electoral register of Croatia. However, during the first years after independence, they were connected to the Slovenian power grid and had Slovenian phone lines. Up until 1984, they had their mail delivered by the Sečovlje post office (subsequently the hamlets inhabitants had to collect their mail at the actual post office in Sečovlje). The Croatian post today delivers to the hamlets, but the inhabitants can still pick up mail across the (factual) border in Sečovlje. Škudelin was connected to the Croatian phone network in 1995, notably with a special local tariff for calls to Slovenia. That tariff, however, expired in 2000 (Pipan 2008: 342) . 4 Croatia, in essence, refers to an accord from July/August 1955 between the Executive Councils of the (Yugoslav) Republics of Croatia and Slovenia according to which mutual consent emerged as to the Dragonja being the border. Both Parties, according to Croatia, "acknowledged and respected the Dragonja River as a boundary between them up until the critical date [25 June 1991]" (PCA Final Award 2017: 230-1, paras 742-3). 5 Slovenia holds that the inhabitants of Mlini and Bužini have refused to be included in the Croatian district of Buje, and that a 1953 survey established the border of the Sečovlje municipality "including three villages on the left bank of the Dragonja" and that the situation was confirmed by the 1964 Act defining the districts and municipalities of the [Yugoslav] Republic of Slovenia (PCA Final Award 2017: 235-6, para 755). 6 Agreement between the Republic of Slovenia and the Republic of Croatia on Border Traffic and Cooperation.

neighbouring countries" (SOPS, Preamble). The agreement represents a number of practical arrangements for (i) local traffic along the land border, and (ii) a joint fishing zone in the respective territorial seas 7 covering approximately 1,200 km 2 . 1,015 km 2 form part of the Croatian territorial sea, and 169 km 2 are located in the Slovenian territorial sea (if measured based on the median line in Piran Bay; interview Croatian senior civil servant, 25-01-2017). It is worth noting, however, that the joint fishing zone has no implications on the delimitation of the common State border (Art. 59 SOPS).

In the EU context, the joint fishing zone under Article 4 of SOPS has made it into the Fisheries Regulation 1380/2013 8 with regard to the access to the territorial waters of Croatia and Slovenia respectively (points 8 and 10 of Annex I of the Regulation). It is crucial to note, however, that the application of the above provisions of the EU Fisheries Policy is subject to the full implementation of the arbitration award (see Sect. 4.4.2) .

Whilst some of its provisions have become obsolete with the EU accession of Croatia (1 July 2013), SOPS has not expired, not least because the border between Croatia and Slovenia remains an external Schengen border. At the time of writing, the last meeting of the Standing Mixed Commission under SOPS took place in Zagreb in December 2016 agreeing on practical measures, such as facilitation of the unhindered cross-border movement of the local population, and repair work on a bridge. The issuance and mutual validation of border-crossing permits at any point of the land border for owners or tenants of cross-border agricultural land appears to continue pragmatically even in the midst of the coronavirus crisis. Although there have been no meetings of the Standing Mixed Commission for more than three years, outstanding issues are resolved through diplomatic channels. However, no agreements have been possible on the repair or reconstruction of cross-border infrastructure, such as a crossborder bridge over the river Kamenica that collapsed during a flooding as early as 2015 (interview senior Slovenian civil servant, 17-04-2020).

What in retrospect turned out to be the most substantial exercise of bilateral diplomacy before 2009 is certainly the Initialled Draft Agreement reached in July 2001. It had been negotiated between the then Prime Ministers Janez Drnovšek (Slovenia) and Ivica Račan (Croatia). The negotiations did not come out of the blue, however. They did build on the previous talks at expert and political level in the 1990s. In addition, the then recent European Commission progress report for Slovenia had mentioned a settlement over the common State border as an outstanding issue (European Commission Progress Report Slovenia 2000: 75) , 9 and the Croatian side seemed aware that Slovenia was located on the road from Croatia to Europe (Arnaut 2002: 44) . More widely, "a lasting partnership on a common Euro-Atlantic path" was part of Račan's motivation (interview Tonino Picula 10 in telegram.hr, 12-01-2018). In addition, a successful deal on the State border was seen as positively influencing the two separate issues of the joint nuclear power station at Krško (the temporary cut-off from electricity supply to Croatia on the part of Slovenia) and Ljubljanska Banka (the reimbursement of foreign currency depositors from SFRY times 11 ; interview senior Croatian civil servant, 19-08-2016; interview Tonino Picula in telegram.hr, 12-01-2018) . 12 It is important to note from a negotiation point of view that, in early 2001, the two Prime Ministers who knew each other from the late days of the Yugoslav Federal State Presidency decided to push away the foreign ministers-notwithstanding the preparatory efforts undertaken by them already in 2000 (interview Alojz Peterle, 28-06-2017)-and tackle the matter personally. The conduct of the negotiations was remarkable as the two Prime Ministers were negotiating over the text and the maps face to face and alone in the room with feedbacks given to their delegations only every couple of hours (interview senior Slovenian civil servant from the then Slovenian negotiating team, 02-12-2016) . 13 On substance, the Drnovšek-Račan 14 Draft Agreement of 17 July 2001 15 "considering that the two States have no territorial claims towards each other" (Preamble) 9 The 2000 European Commission Report on Slovenia can be found at https://www.esiweb.org/pdf/ slovenia_EC-Slovenia%20regular%20report-2000_en.pdf. 10 Tonino Picula MEP was Foreign Minister of Croatia 2000 Croatia -2003 Many citizens' private foreign-currency deposits were illegally used by the Yugoslav State to cover its demand for foreign-currency reserves. For the SFRY banking system and its need for foreign currency reserves see e.g. Hojnik and Mevel (2016: 10-11) . 12 The financial compensation aspect of the Krško dispute was solved in December 2015 by means of investor-State arbitration, see Arbitral Award ARB/05/24 HEP vs. Slovenia (http://icsidfiles. worldbank.org/icsid/ICSIDBLOBS/OnlineAwards/C69/DC7132_En.pdf). The Ljubljanska Banka case was to some extent, solved through the Ališič judgement (http://www.vlada.si/fileadmin/ dokumenti/si/projekti/2015/Varcevalci/Grand_Chamber_judgment_Alisic_and_Others__Old_ foreign_currency_savings_deposited_in_SFRY__2___1_.pdf) of the European Court of Human Rights of July 2014 ordering Slovenia to take care of the compensation. The issue of burden-sharing between the SFRY successor States, however, is subject to voluntary pluri-lateral negotiations (interview senior Slovenian civil servant, 2-12-2016). 13 A semi-comparable bilateral line-up, from a purely negotiations-technique point of view, was perhaps the one between Vaclav Klaus and Vladimir Mečiar when they were negotiating the terms of the dissolution/separation of theČSFR into the Czech Republic and the Slovak Republic in the late summer of 1992 (interview Tomáš Prouza, State Secretary in the Foreign Ministry of the Czech Republic in charge of EU affairs , 18-09-2017 interview Eduard Kukan MEP, Foreign Minister of Slovakia 1998 , 03-10-2017 . 14 In alphabetical order. In Croatia, the Draft Agreement is usually referred to as English translation by the Slovenian Foreign Ministry of the text initialled by the two heads of the negotiating delegations. For a copy of the initialled Slovenian original see Appendix D.

represents a fully negotiated settlement and a solution sui generis with a number of striking features:

As for (i) the delimitation at Piran Bay and in the Gulf of Trieste, the lateral border goes from the outfall of the Dragonja River (St. Odorick's Canal) to the point (on the former SFRY closing line of the Bay; PCA Final Award 2017: 272, para 880) which is one fourth of the distance between Cape Savudrija (the Croatian entrance to the Bay) and Cape Madona (the Slovenian entrance at Piran). As a result, roughly four fifths of the Bay go to Slovenia and one fifth goes to Croatia [Article 3(1)]. Remarkably, the Final Award of the later arbitration procedure took up this very delimitation line inside the Bay on the basis of the fishing management and factual police patrolling during the period up until 25 June 1991 (PCA Final Award 2017: 279, paras 912-3; see "The Bay" in Sect. 4.3.5.2).

From the above point at the mouth of the Bay, the border turns south and runs in an east-west parallel line up to the former Yugoslav-Italian sea border from 1975 16 except for the tiny strip foreseen for the junction to the high seas [Article 3(1)]. Article 3 is silent on the nature of the respective waters inside the Bay. However, as the line over the mouth of the bay is not expressly referred to as the closing line, it appears that the status of the waters inside the Bay is considered the respective territorial sea (as opposed to internal waters). 17 In respect of (ii) access to the high seas for Slovenia, a novel approach was agreed on: a "junction" between the territorial sea of Slovenia and the high seas via a high-seas corridor through the Croatian territorial sea [Article 4(1) ]. The width of the junction is 2.3 nm (Article 4(2); see also PCA Final Award 2017: 340, para 1060). As a by-product, the corridor created a triangular enclave of Croatian territorial sea maintaining the country's sea border with Italy (Article 5). It must be noted that no sovereign rights were accorded to either State as for the corridor's water column, its seabed and its subsoil [Article 4(5) ]. In terms of the international law of the sea, a corridor between the territorial sea of a State and the high seas historically only emerged twice before (in a pluri-lateral treaty on free passage through The Sound/Øresund, one of the Danish straits, in 1857, 18 and in an agreement between France and Monaco in 1984; for the latter see Arnaut 2002: 50) , and a quasi-extraterritorial triangle strip of territorial sea certainly was unheard of at the time and still is today (see Fig. 4 .2). 16 Treaty of Osimo 1975 delimitating the territorial waters of Italy and Yugoslavia. Both Slovenia and Croatia have declared to inherit the respective sea border strip of Yugoslavia. Italy did not object (Cataldi 2013: 1; Klemenčić and Topalović 2009: 313-4) . For the Osimo Treaty see Sect. 2.4.3. 17 It is important to note that, unlike in the territorial sea, there is no right to innocent passage for foreign vessels in internal waters (see Tanaka 2015: 78-81; Rothwell and Stephens 2016: 55-9) . 18 The pluri-lateral treaty was concluded between Denmark and Austria, Belgium, France, Great Britain, Hanover, the Hanse Towns, Mecklenburg-Schwerin, the Netherlands, Oldenburg, Prussia, and Sweden-Norway. A second bilateral treaty was concluded between Denmark and the United States. Strictly speaking, the provisions only apply to the signatories, but Danish State practice has rendered the provisions a quasi-universal regime (see Bangert 1997: 105-7) . As for (iii) the land border, the Three Hamlets south of the Dragonja were finally accorded to Croatia, to name one prominent example. 19 All other disputed spots along the border, such as Trdinov Vrh/Sveta Gera, or the Hotiza-Sveti Martin area along the Mura River, were resolved, too. Annex II of the Draft Agreement contains a verbal description of the border linking 85 points from the tripoint at the border to Hungary to the outfall of the Dragonja into Piran Bay (see Appendix C).

One peculiarity of the Draft Agreement is worth mentioning from a point of view of its authenticity. In the provisions on both the land border and the sea border, reference is made to the verbal description in Annex II prevailing over the maps and coordinates respectively [Articles 3(3) and 4(4)]. Usually, maps and coordinates take precedent over verbal descriptions in the application of a treaty.

It is vital to note that the Initialled Draft Agreement never entered into force. The Foreign Affairs Committee of the Croatian Parliament rejected the text, so it never underwent ratification in the Sabor (PCA Final Award 2017: 27, para 92; letter from Račan to Drnovšek, 3 September 2002) .

In retrospect, several reasons may be identified for the failure of the Drnovšek-Račan Draft Agreement:

(i) The agreement may, on its substantive provisions, have been too innovative, and there were legal doubts as to whether a Croatian triangle enclave disjointed from the rest of the Croatian territorial sea, an unprecedented solution sui generis, would be recognized by Italy (Arnaut 2014: 149 ; see also Grbec 2015: 176) ; (ii) Virtually the entire Croatian legal expert establishment was against the text, not least because they had all favoured a delimitation line approximating the equidistance line as for the delimitation in the Bay. What is more, it appears that none of the law-of-the-sea experts in Croatia were consulted ahead or during the secret negotiations (interview Vladimir-Ðuro Degan, 21-11-2019) . Then again, one could argue that the likelihood of reaching any kind of agreement at all would have been virtually at zero "had there been a greater audience" (interview Vesna Pusić, 24-02-2017 ); (iii) Drnovšek, having secured the support of the opposition (mainly Janša's SDS) on his part, had overestimated the command of domestic support for the deal on the part of Račan (interview senior Slovenian civil servant from the then Slovenian negotiating team, 02-12-2016). Račan had indeed failed to persuade all coalition parties, most notably Budiša's HSLS (interview Vesna Pusić, 24-02-2017) , and the major opposition party HDZ (interview Ivo Sanader, 19-05-2016) . 20 It must be noted in this context that the then government comprised no less than six parties, the first-ever coalition government in Croatia after three consecutive HDZ majority governments, and that by summer 2001, Račan's decision to extradite generals Gotovina and Ademi to the ICTY had provoked the resignation of the HSLS ministers and a subsequent vote of confidence (Dolenec 2013 : 150-1) 21 ; (iv) The traumatic experience on Croatia's other borders with Serbia and Bosnia-Herzegovina between 1991 and 1995, together with the territorial shape of Croatia, had created a solid sensitivity towards territorial issues (interview Dejan Jović, 02-11-2017 ; see also Klemenčić and Schofield 1995: 71-2) , in particular with regard to the Homeland War (see Koska and Matan 2017: 129-131; Lamont 2015: 72-74) during which Croatia lost around 20,000 lives (all told, military and civilian deaths ; Jović 2011: 36) . The repercussions of the Homeland War led to the Sabor Declaration from October 2000 stating that the country "led a just and legitimate, defensive and liberating, and not an aggressive and conquering war […] in which it defended its territory […]", and that therefore " [t] he fundamental values of the Homeland War are unambiguously accepted by the entire Croatian people and all Croatian citizens" (Official Gazette of the Republic of Croatia, No. 102/2000); see Sect. 2.5.2. 20 Račan called Sanader on 29 July 2001, 12 days after the initialling of the Draft Agreement, when the HDZ chair was already on summer vacation with his family on Lopud island. The two spoke for three quarters of an hour. 21 What aggravated the problem of the diversity within the six-party coalition was the fact that HSLS chair Budiša and HSS (Croatian Peasant Party) chair Tomčić were not serving as government ministers which required additional coordination efforts outside the government structures.

In September 2002, Račan sent a passionately gloomy letter to Drnovšek in which he summed up the spirit of the preceding months: […] I am certain that you hold that the friendly relations and cooperation between our countries are the strategic interest of both our countries and peoples, and that for democratic forces there cannot be an alternative. However, things are not going in that direction.

Arguments and forces of conflict are gaining momentum on both sides of the joint border and are using open and unsettled issues between our countries, making them bigger and bigger and ever harder to settle. We are facing the risk of unreasonable extension of the problems and conflicts between our countries to our relations where such problems did not previously exist. It would be absurd if today Slovenia and Croatia 'balkanized' their relations and State policy, considering that such a way to 'settle' problems is losing ground throughout Southeast Europe […] .

As a failed attempt, the initialled Draft Agreement cannot be a basis for settling the problem […] It was an attempt without legal effects […] . We can, and therefore we must, reconsider what to do under the circumstances. It appears that, concerning the border, we cannot reach a solution amicably and of our own accord […] . The most reasonable solution that remains is, therefore, arbitration. I am prepared to talk with you about binding arbitration, after I obtain support from the Croatian Parliament. (Letter from Račan to Drnovšek, 3 September 2002) After 2001, a bilaterally negotiated agreement clearly seemed out of reach (see also Petrič 2017: 364) . Indeed, no efforts to solve the outstanding border issue were indeed made over the next five years.

Only in the summer of 2007 was a new attempt at a solution made. The Slovenian Prime Minister Janez Janša and his Croatian counterpart Ivo Sanader met in Bled on 26 August and agreed to submit the dispute to the International Court of Justice (ICJ). Janša, on his part, had not consulted anyone prior to his decision to move away from the Draft Agreement of 2001 (which was the result of intensive bilateral negotiations) and refer the matter of dispute to an international court instead (interview senior Slovenian civil servant from the 2001 Slovenian negotiating team, 02-12-2016) . Some indeed saw the Bled Agreement as a pragmatic, but forward-looking "backpedalling exercise" in respect of the bilateral Drnovšek-Račan deal (interview Davor Stier, 23-09-2015) .

The Bled Agreement tasked a joint team of legal experts with the drafting of the mandate for the Court. That mandate was supposed to be discussed in both parliaments in a cross-party spirit and ready for submission to the ICJ by the end of 2007 (Office of the Prime Minister of Slovenia's tape-recording transcript of the Janša statement at the press conference, 26 August 2007: 1). The joint understanding was such that the mandate for the ICJ was also to be ratified by both parliaments (interview Ivo Sanader, 02-11-2017) . It is worth noting that, unlike Drnovšek-Račan in 2001, there was no intended link to the other two issues Krško and Ljubljanska Banka. Rather, "the very fact that we have decided to involve a third party in settling the border issue, and to continue to solve other issues bilaterally, shows that we are not dealing with packages" (Janša tape-recording transcript, 26 August 2007: 2). However, the above timetable proved too ambitious as the travaux préparatoires for the mandate for the ICJ turned out to be a rocky road. Drafts were exchanged following a joint meeting of the expert groups in June 2008. 22 Somewhat unexpectedly, the disagreement over which judicial body exactly the dispute was supposed to be submitted to re-surfaced. This is evident from a Slovenian draft of the Special Agreement, the mandate for the judicial body, where reference is made to three options ("International Court of Justice in The Hague/Permanent Court of Arbitration/Ad-hoc Arbitration") in virtually any of the draft articles (Special Agreement, September 2008). Articles 1 and 2 shall suffice as an example:

Article 1

Submission of a dispute The Parties agree to submit the dispute to the Permanent Court of Arbitration.

Option 3:

The Parties agree to submit the dispute to Ad-hoc Arbitration.

Article 2

The Parties authorize the Court/Permanent Court of Arbitration/Ad-hoc Arbitration to adjudicate on the substantive elements of the dispute regarding the determination of the lateral boundary between the maritime belts of the two Parties and a more precise delimitation of the land border […] . (Special Agreement, September 2008; emphasis added) Conversely, a Croatian draft solely referred to the ICJ (Special Agreement between the government of the Republic of Croatia and the government of the Republic of Slovenia on the submission of the boundary dispute between the two States to the International Court of Justice, September 2008) as becomes clear in the respective first two articles:

The parties agree to submit the dispute to the International Court of Justice […] .

Article II 1. The Court is requested to determine, in accordance with the principles and rules of international law (as applicable in the matter between the Parties) […] . (Special Agreement between the government of the Republic of Croatia and the government of the Republic of Slovenia, September 2008) 22 The initial deadline of December 2007 had proved unattainable. In the context of the entry into force of the Croatian ZERP (see Sect. 3.1.4.4) in early March 2008, Janša and Sanader agreed to intensify the work on the mandate and to refrain from provocations in Piran Bay (interview Ivo Sanader, 02-11-2017 ).

There were three meetings altogether, and by early 2009, the positions had not changed. Slovenia withdrew its members from the expert groups in March 2009 (interview senior Slovenian civil servant, 17-10-2016; see also PCA Final Award 2017: 31, para 103). Slovenia holds that "the mandates of the negotiating delegations were obviously very different" (interview senior Slovenian civil servant, 17-10-2016). It must not be overlooked in this context, however, that the EU accession negotiations of Croatia had already been heavily affected by the Slovenian "reservations", 23 and that the initial European Commission initiative to forge a deal on mediation or arbitration was already in full swing (see Sect. 4.2.2) . In the same vein, the legal-political dispute over the Croatian Ecological and Fisheries Protection Zone (EFPZ/ZERP) and the Slovenian Ecological Protection Zone and Continental Shelf (EPZCSA) between 2003 and 2008 had seriously added to the bilateral tensions over the sea border (see Sect. 3.1.4.4) .

The disagreement on substantive issues of the mandate for judicial adjudication is exemplary for the loaded task of negotiating the mandate. The failure of the Bled Agreement is a case in point. As Keohane et al. note , the legal norms and requirements as the core issues of a mandate tend to be precisely fixed. Thus, the fiercest kind of bargaining usually ensues over the terms of a prospective settlement by a third-party judicial body (Keohane et al. 2000: 461-2; 470) .

At this point, it is worth looking at the operational design of the workings of the European Union accession negotiations, the bodies involved, their roles, and the relevant procedural steps.

Generally, any EU enlargement process starts with the application for membership of the potential Candidate Country. 

As a general rule, the pace of accession is linked to the pace of goal attainment (mostly meaning reforms) on the part of the Candidate Country. It is worth contemplating, however, that the applicable methodology for the operational accession negotiations has changed considerably over time, reflecting developments both inside the EU and in Candidate Countries.

(i) The fundamental conditions for EU accession after the accession of Austria, Finland, and Sweden in 1995 26 are laid down in the so-called Copenhagen Criteria set out in 1993:

• Political criteria: stability of institutions guaranteeing democracy, the rule of law, human rights and the respect for and the protection of minorities; Kukan, 27-09-2017) . 26 For previous EU enlargement rounds see e.g. Emmert and Petrović (2014) or Preston (1995) .

• Economic criteria: a functioning market economy and the capacity to cope with competition and market forces; • Administrative and institutional capacity to effectively implement the EU acquis and the ability to take on the obligations of EU membership (Presidency Conclusions European Council Copenhagen, 22 June 1993: 13; emphasis added).

(ii) There have been a number of crucial additional requirements for the accession criteria introduced more recently:

• Priority is given to the rule-of-law Chap. 23 (judiciary and fundamental rights) and 24 (justice, freedom and security). These Chapters are to be tackled at an early stage of the accession negotiations (European Commission Enlargement Strategy, 12 October 2011: 23 It must be noted that this new Commission strategy, known as the new approach, reflects the experience with Croatia's accession negotiations and may be seen as (i) marking a sea-change in terms of Chapter re-prioritization, and (ii) putting more focus on "monitor[ing] progress with increased attention" (European Commission Enlargement Strategy, 12 October 2011: 23; interview Member State E COELA civil servant, 21-10-2016; interview Member State H COELA civil servant, 07-03-2018). The new approach, more recently and colloquially termed "fundamentals first" (e.g. European Commission Enlargement Strategy, 9 November 2016: 2), became operational at the beginning of the EU accession negotiations with Montenegro on 29 June 2012. It has since been applied in the same vein also to the negotiations with Serbia, which started on 21 January 2014. 27 The focus of attention has since been on implementation of the rule-of-law Chapters on the ground, i.e. the so-called track record. "We have recently started to focus on the actual output of judicial systems. And that output is indeed quantifiable. In fact, one can look at the ratio between the number of investigations, the number of actual charges resulting from them, and whether the court handed down a judgement." To that end, expert groups are selected by the Commission and composed of practitioners who work alongside their full-time occupation and gather information on the ground. Some of the expert groups' findings ("case-based peer reviews") tend to be incorporated into the interim benchmarks proposed by the Commission later on (interview European Commission civil servant, 10-01-2018). However, it is the view of this author that there is a shortcoming with the track-record approach: Quantifiable as one selected item may be, there is no definition of track record in terms of what kind of performance in what areas exactly is going to be measured over what time period. Miščević and Mrak (2017: 196-7) argue that the new emphasis on Chaps. 23 and 24, not least by the introduction of the interim benchmarks, renders these two Chapters "the role of 'controller' of the negotiations". As a result, Member States increasingly shaped these negotiations by setting benchmarks and deciding whether they "have been met or not". In fact, this analysis appears to neatly correspond to contemporary State practice in the Council Working Group on Enlargement (COELA). A practitioner's view is that "interim benchmarks actually tend to be worded in a way that they can never be met" (interview Member State H COELA civil servant, 07-03-2018).

(iii) In its Enlargement Strategy from February 2018, the European Commission crafted some further fine-tuning of the new approach introducing a few new features:

• A strong emphasis on the rule of law, in particular the "independence, quality and efficiency of the judicial system", and the fight against corruption and organised crime (European Commission Enlargement Strategy, 6 February 2018: 4); • Narrower provisions on bilateral disputes. These are supposed to be "solved as a matter of urgency". Where this proves impossible on a bilateral level, "parties should submit them unconditionally to binding, final international arbitration" (European Commission Enlargement Strategy, 6 February 2018: 7). Notably, there was a diplomatic battle on the above wording between the Croatian and the Slovenian Commissioner during the late drafting stage. At some stage of the drafting, the International Court of Justice was also mentioned in brackets, and that issue was hotly debated (information obtained from several Commissioner's Cabinet members in March 2018; draft version of the 2018 Enlargement Strategy from November 2017 this author has seen). The final wording, however, is unusually and unnecessarily fuzzy and confusing, and clearly indicates that it is a compromise formula 28 ;

• An indicative EU accession target date of 2025 has been set for Serbia and for Montenegro. Whilst the Commission hastens to add that such date "is purely indicative and based on the best-case scenario" (European Commission Enlargement Strategy, 6 February 2018: 7), it is there nevertheless and thus goes against the grain of a purely merits-based approach, the Commission's very mantra from recent years; • More emphasis on "soft" ("socio-economic") issues (European Commission Enlargement Strategy, 6 February 2018: 12). To that end, the funds for the "Erasmus+" programme should be "doubled to help even more young citizens of the Western Balkans to study and gain experience in the EU" ( It was not lost on connaisseurs of EU enlargement either that there was a new momentum in the European Commission's enlargement approach. That new dynamism appears to have been taken up subsequently by the European Commission's Candidate Country status reports (formerly known as progress reports) from April 2018. The Commission's reports actually include the recommendation to start accession negotiations with Albania and Macedonia. However, there was an intense debate in the college of Commissioners on 17 April 2018 as to whether to actually recommend such a start (information obtained from several Commissioners' Cabinet members, 17-04-2018) as the President of France had mentioned a little earlier during his plenary speech in the European Parliament on the morning of the same day, that EU reform had to take precedence over EU enlargement (author's field notes, 17-04-2018).

As reservations with regard to EU enlargement on Member State level were, and in fact are, not limited to France, a (temporarily) face-saving solution had to be found. The General Affairs Council (EU foreign ministers) on 26 June 2018 did in principle endorse the positive recommendation from the European Commission. Yet, it postponed the actual beginning of accession negotiations for Albania and Montenegro to June 2019 subject to domestic implementation of reform and subsequent Council approval. In return, the technical screening process carried out by the European Commission, somewhat opaquely termed "necessary preparatory work" in the Council Conclusions, was to start immediately which it did (General Affairs Council Conclusions, 26 June 2018: 16, para 44 [FYR Macedonia]; 19-20, para 54 [Albania] ; interview European Commission civil servant DG NEAR, 28-08-2018).

However, resistance remained resilient and the June 2019 General Affairs Council (GAC) was unable to live up to its promise from one year ago to give the green light. Even the GAC of 15 October 2019 was not able to produce a text. A few days later, the European Council of 17/18 October 2019 hotly debated the issue. Enlargementcritical Member States such as Denmark or the Netherlands would have been ready to decouple the starting dates, i.e. to give the green light to North Macedonia and to postpone Albania with a reference to the existing merits-based approach. France, however, would block any opening of negotiations altogether regardless of North Macedonia fully meeting the EU criterion of settling the name dispute with Greece by means of the historic Prespa Agreement 29 (author's field notes, 17-10-2019). As a result, the Conclusions of the European Council constitute the shortest-ever wording on enlargement in the history of the EU to date and are worth quoting:

The European Council will revert to the issue of enlargement before the EU-Western Balkans summit in Zagreb in May 2020. (European Council Conclusions 17/18 October 2019: 2) (iv) In the light of the French reform demand and proposal 30 for a new methodology for EU accession negotiations, the European Commission presented a revised Enlargement Strategy labelled "A credible EU perspective for the Western Balkans" on 5 February 2020. 31 Building on the merits-based approach, the new "reinvigorating" elements are:

• Regaining and increasing credibility through "Western Balkans leaders […] deliver[ing] more credibility on their commitment" with regard to fundamental reforms, whilst at the same time the "European Union delivers on its unwavering commitment to a merits-based process" which, notably, includes 29 For the Prespa Agreement see Sect. 6.4.1. 30 In November 2019, France submitted a non-paper on "Reforming the European Union accession process" calling for (i) gradual accession to the EU including the reversibility of negotiations, and (ii) stronger political governance. The main novelty was to introduce "several successive stages" along "coherent policy blocks" (stage 1: rule of law, fundamental rights, justice and security, comprising Chaps. 23 and 24; stage 2: education, research and space, youth, culture, sports, environment, transport, telecommunications and energy, relating to Chaps. 14, 15, 21, 22, 26, 25, 27; stage 3: employment, social policy, health and consumer protection, competitiveness, based on Chaps. 19, 28, 5, 7, 8, 20; stage 4: economic and financial affairs, subject to Chaps. 4, 9, 16, 17, 18, 32; stage 5: internal market, agriculture and fisheries, comprising Chaps. 29, 1, 2, 3, 6, 10, 11, 12, 13 that "all parties must abstain from misusing outstanding issues in the accession process" 32 (European Commission Enlargement Strategy, 5 February 2020: 2); • "Stronger political steer" through, for instance, Member States contributing through monitoring on the ground as for the situation in Candidate Countries and by means of feeding in observations to the European Commission annual reports, and the European Commission "including proposals for corrective measures […] for approval by Member States" in the annual reporting (European Commission Enlargement Strategy, 5 February 2020: 3; emphasis added); • "A more dynamic process" with the novelty of grouping negotiating chapter in clusters. 33 The chapters are subdivided into six clusters. Notably, all chapters of a cluster will be opened as a whole (as opposed to the individualchapter basis applied previously Fundamentals" comprising Chaps. 23, 24, 5, 18 and 32; "Internal Market" relating to Chaps. 1, 2, 3, 4, 6, 7, 8, 9 and 28 ; "Competitiveness and inclusive growth" with regard to Chaps. 10, 16, 17, 19, 20, 25, 26 and 29 ; "Green agenda and sustainable connectivity" with Chaps. 14, 15, 21 and 27; "Resources, agriculture and cohesion" comprising Chaps. or market access (European Commission Enlargement Strategy, 5 February 2020: 5-6).

Whilst the 2020 Enlargement Strategy maintains the merits-based approach, the main innovation appears to be the clustering of negotiating chapters and an increased emphasis on positive and negative conditionality. Despite the fact that, at the time of writing, it was as yet impossible to make a preliminary assessment of the operational workings of the new methodology, there nevertheless is some obscurity with the following issues: First, whilst there is the provision of reverse qualified-majority voting on Commission proposals executing the response to a negative reform performance, no provisions exist as of yet on proposals for accelerated phasing-in to EU policies or increased pre-accession funding. 36 Second, there is no clear mention of the fact that, as all parties are supposed to abstain "from misusing outstanding issues", bilateral disputes between a Member State and a Candidate Country must be solved ahead of accession, a key provision in the 2018 Enlargement Strategy (see above).

The dynamics with regard to opening accession negotiations with North Macedonia and Albania changed in the aftermath of the new European Commission methodology. In fact, France withdrew its reservations and the General Affairs Council (GAC) of 24 March 2020 endorsed the new methodology and reached a political agreement to open negotiations with Albania and North Macedonia. 37 The relatively swift decision may, however, also be related to a certain sense of urgency and the desire to send a signal of political solidarity and moral support during the emerging coronavirus pandemic 38 where some Western Balkan countries, in particular Serbia and Montenegro, had received some substantial, badly-needed medical equipment support from China (author's field notes March and April 2020; see also Stjepčević, 4 April 2020; Vuksanović, 8 April 2020) in a "humanitarian aid blitz" (Myers and Rubin, 18 March 2020) whilst some EU national governments were discussing or even executing domestic export bans for medical equipment (see e.g. Gostyńska-Jakubowska and Scazzieri, 23 March 2020).

The substantive issues are dealt with at the operational level of the accession negotiations, i.e. when the question of opening and/or closing of negotiation Chapters arises. 36 The European Parliament expressed its concern about a lack of clarity with regard to the reversibility of the accession process calling for "objective criteria when deciding whether negotiations should be put on hold or suspended" (European Parliament Resolution 19 June 2020: 6). 37 The GAC invited the Commission to draft the negotiation frameworks (GAC Conclusions 24 March 2020: 3-5). The Commission presented the drafts on 1 July 2020 scheduled for adoption by Council before the end of the year. 38 Council and other meetings switched from physical gatherings to video-conferencing in mid-March 2020.

In a nutshell, the process is as follows (fundamentals-first version as operational since 29 June 2012):

• It is useful to note that for rule-of-law issues (Chaps. 23 and 24) the Commission operates a biannual non-paper reporting system to inform the Member States on progress in the field. In addition, the Commission proposes interim benchmarks (including updated ones) for Chaps. 23 and 24 matters if they consider it necessary (see e.g. Council of the European Union, DCP on Chap. 24, accession negotiations with Serbia, 5 July 2016: 22-32).

As both the opening and interim benchmarks are proposed by the Commission and are not debated in COELA, it is up to Member States to individually lobby the Commission on the need and potential content of such benchmarks. The Commission's DCP, however, is more or less openly debated and amended inside COELA 

The border dispute with Slovenia was by no means new in the context of Croatia's EU accession process. It had already featured prominently, albeit somewhat in the subtext perhaps, during the introduction and adaptation of the Croatian ecological protection zone in the Adriatic (ZERP) between 2003 and the spring of 2008 (see Sect. 3.1.4.4) . However, the border issue only fully impacted the ongoing accession negotiations with Croatia after the Slovenian EU Presidency (which the country held during the first half of 2008) and after the Bled Agreement of August 2007 had begun to run dry due to the once again diverging views on what type of third-party judicial body should be entrusted with the management of the border issue, a dispute that was meant to be overcome by the very Bled Agreement itself in the first place (see Sect. 4.1.5). 39 The Stabilisation and Association Process was launched in 1999 as a tool of support particularly designed for the so-called Western Balkans countries. It contains (i) a bilateral (EU and applicant country) Stabilisation and Association Agreement (SAA) which usually marks the beginning of the EU accession process, (ii) free trade agreements with the EU, (iii) financial assistance, and (iv) the promotion of regional cooperation and good neighbourly relations. For a comprehensive overview of the SAA process see e.g. https://ec.europa.eu/neighbourhood-enlargement/policy/glo ssary/terms/sap_en. 40 https://www.consilium.europa.eu/en/meetings/international-ministerial-meetings/2017/06/20/.

During October 2008, the Slovenian approach of blocking the ongoing EU accession negotiations with Croatia in a number of areas fully materialized (interview Member State B civil servant working in COELA at the time, 08-12-2016). The actual decision to bring the matter of the prejudging documents to the negotiating table had been taken by the Slovenian government in June 2008 just before the end of the Slovenian EU Council Presidency. 41 The decision was implemented in October of that year, very close to polling day in Slovenia (interview senior Slovenian civil servant, 24-01-2017). The Slovenian "reservations" concerned eleven negotiating chapters on the grounds that the documents submitted by Croatia "prejudice[d] the definition of the border between Slovenia and Croatia" (Information on prejudices in certain negotiating chapters of accession negotiations for Croatia's membership of the EU, Slovenian non-paper, 18 December 2008: 1; see also PCA Partial Award 2016: 3).

In fact, the Slovenian veto was grouped into three categories and applied to (i) the opening of five Chapters (11 Agriculture and rural development; 12 Food safety, veterinary and phytosanitary policy; 16 Taxation; 22 Regional policy and coordination of structural instruments; and 24 Justice, freedom and security); (ii) the provisional closing of two Chapters (21 Trans-European networks; and 29

Customs union); and, due to "additional substantive reservations"; (iii) the opening of Chaps. 4 (Free movement of capital), 13 (Fisheries), 27 (Environment), and 31 (Foreign, security and defence policy; Slovenian non-paper, 18 December 2008: 1).

The reservations in the Slovenian paper can be outlined as follows: In Chap. 4 (Free movement of capital), Slovenia does not accept the total area of land under the Croatian Programme of management of State-owned agricultural land, as had already been protested bilaterally (Slovenian non-paper, 18 December 2008: 1-2). As for Chap. 11 (Agriculture and rural development), Slovenia protests against the Territories of Counties, Cities and Municipalities Act, a separate Croatian law to the Local and Regional Self-Management Act mentioned in the Croatian negotiating position, for incorporating the Three Hamlets on the left bank of the Dragonja River (Slovenian non-paper, 18 December 2008: 2; see also Sect. 4.1.2.2 and PCA Final Award 2017: 240-241, paras 767-770). On Food safety, veterinary and phytosanitary policy (Chap. 12), Ljubljana objected since the Croatian rules on veterinary checks and control of animal products in cross-border trade are related to the Croatian 41 It is established custom and practice on the diplomatic scene in the EU that the rotating Council Presidency refrains from actively advancing matters considered an own national interest. Council Presidencies naturally take on a facilitating role in whatever EU decision-making is due during their Presidency.

Customs Act containing a reference to the Croatian Maritime Code 42 (Slovenian non-paper, 18 December 2008: 2).

In the Fisheries Chapter (13), Slovenia protests against a number of laws and implementing regulations expressly mentioning the Croatian ZERP, the equidistance line in Piran Bay, and the CS boundary with Italy (Slovenian non-paper, 18 December 2008: 2-3; see also Sects. 3.1.4.4 and 3.1.5). With regard to Taxation (Chap. 16), Ljubljana objects to the Croatian Public Roads Act as, in its recent implementing Decree, the Plovanija-Sečovlje border crossing was not listed as "provisional" (as had been agreed on in a 1994 bilateral act; see also Sect. 4.1.2.2) thus predetermining the common State border. In the Trans-European Networks Chapter (21), Slovenia criticises Zagreb's National Programme for the Development of Railway Infrastructure as it contained maps of the Croatian view of the maritime boundary with Slovenia. As for regional policy and coordination of structural instruments (Chap. 22), Slovenia objects to the Croatian Contingency Plan for Accidental Marine Pollution, referring to the maritime border in the annexed map (Slovenian non-paper, 18 December 2008: 3). With regard to Chap. 24 on Justice, freedom, and security, analogous to the Croatian Decree in Chap. 16, the Sečovlje-Plovanija border crossing is listed as a permanent installation (Slovenian non-paper, 18 December 2008: 3-4; see also Sect. 4.1.2.2) .

In relation to Environment (Chap. 27), the Contingency Plan for Accidental Marine Pollution is mentioned as is its annexed map (as with Chap. 22). Further, Zagreb's Decree on air quality in inhabited regions, the National Air Quality Protection and Improvement Plan, and the National Strategy on Water Management, contained several maps with the sea border. Lastly and with regard to Chap. 29 (Customs union), there is a protest against the Customs Act since it contained a reference to the Croatian CS "den[ying] Slovenia the possibility of [a] continental shelf" (Slovenian non-paper, 18 December 2008: 4; see also Sects. 3.1.4.4 and 3.1.5).

Nevertheless, the Slovenian reservations did not lead to a complete standstill in the Chapters concerned, as the screening of the Croatian legislation by the European Commission continued at expert level, so that the overall delay was marginal. Further, other Chapters were opened or provisionally closed as foreseen. The tactics of Slovenia were widely considered strategically and skilfully deployed, ranging from debates at ministerial level to behind-the-scenes action such as removing points from the agenda of the Council Working Group COELA. However, the Slovenian case was "a novelty of a country using its status of Member State to enforce its position vis-à-vis a Candidate Country" (interview European Commission civil servant involved in the accession negotiations with Croatia, 07-01-2016) although it was a purely bilateral issue. As a Member State diplomat put it: "The border dispute between Slovenia and Croatia was deeply political, but it is not a part of the accession process" (interview Member State J civil servant who worked in COELA in 2009 COELA in , 19-10-2016 .

The reaction amongst EU Member States was predominantly unenthusiastic in the Council Working Group (interview Member State A civil servant, 23-06-2016). Behind the scenes, "a lot of good-will was lost as the Slovenes had played it rather clumsily by not putting much effort into explaining the situation. The issue got on the nerves of a large number of Member States despite the fact that the spirit in COELA remained professional and no national position was taken personally" (interview Member State B civil servant, 08-12-2016; both civil servants worked in COELA in 2008/09). There was very little support for the Slovenian position, and, accordingly, the French EU Presidency initially took a firmly critical stance towards Ljubljana's position (interview European Commission civil servant involved in the accession negotiations with Croatia, 07-01-2016; interview Member State C civil servant who worked in COELA 2008 COELA /2009 COELA , 27-01-2017 . The very few Member States who tacitly supported the Slovenian move saw Ljubljana's call for access to the high seas as being somewhat justified in a wider historical context of the northeastern Adriatic where full maritime access for the area of present-day Slovenia was natural under the pre-1918 Habsburg rule and during post-World-War-II Yugoslavia (interview Karel Schwarzenberg, 43 26-09-2017) .

Croatia considered the Slovenian approach unfair and out of proportion as most of the implementing regulations were not part of the Croatian accession documents. The Slovenian reservations had therefore had to be largely based on additional Slovenian screening of Croatian implementing legislation including legal acts three levels down with regard to the legislation referred to in the original Croatian negotiating position. Furthermore, the Slovenian position was perceived as being shared by the other Member States. "There was no outrage, and this appeared to us as a sign of solidarity amongst the members of a club. We felt all this was a manipulation of the Croatian accession negotiation process" (interview member of the then Croatian negotiating team, 30-11-2015) . On a lighter note, "Slovenia was not fully supportive of Croatia during our accession negotiations, although they had a great knowledge, expertise, and understanding of Croatia" (interview Vesna Pusić, 24-02-2017) .

France had taken over the EU Council Presidency from Slovenia on 1 July 2008. In the later stages of its Presidency, France actively pursued defusing the conflict at ambassador level, i.e. to work out a solution in trilateral meetings (interview civil servant involved in the trilateral meetings, 27-01-2017; Internal note Ministry of Foreign Affairs Croatia 2012: 2). The situation proved fairly tense, first of all for the accession negotiations as such as the Slovenian reservations had a "systemic effect" on the preparation of the DCPs (see Sect. 4.2.1.2), and secondly "there was a real and open confrontation" between Croatia and Slovenia (interview civil servant involved in the trilateral meetings, 27-01-2017).

The idea of the French diplomacy was to have an exchange of letters between the Council Presidency and Croatia to defuse the prejudging nature of some of the Croatian accession documents towards the common State border. This approach was to address the Slovenian concerns and was supposed to remove the blockade. There was a series of trilateral meetings at the French Permanent Representation, the Slovenian Permanent Representation, and the Croatian Mission in Brussels respectively in which drafts were discussed. They culminated in a non-official "Presidency's proposal" from 15 December 2008 which is worth quoting:

1. Letter from the Presidency of the EU Council to Croatia:

The Presidency of the EU Council underlines that the purpose of this exchange is to address the question of any border prejudice, by confirming that the accession negotiations between the EU and Croatia will not in any way prejudice the final resolution of the border issue between Slovenia and Croatia and the positions of both sides, in any procedure relating to the resolution of the border issue.

On this basis, the Presidency […] confirms that no statement made by Croatia in the context of its accession negotiations to the EU, when related to the border between Slovenia and Croatia, may be relied upon by Croatia in any procedure relating to the settlement of the border issue between Slovenia and Croatia in such a way as to imply acceptance or recognition of such statement by any Member State of the EU. In addition, the fact that Slovenia agrees, following its internal procedures, the EU documents and positions which refer to or summarize Croatian documents and positions, related to the border issue between Slovenia and Croatia, cannot be interpreted, in any procedure relating to the settlement of the border issue, as committing Slovenia and its position regarding this issue.

The above applies to all documents and positions either written or submitted orally, including, inter alia, maps, negotiating positions, legal acts and other documents in whatever form, produced, presented or referred to by Croatia in the framework of the EU accession negotiations. It also applies to all EU documents and positions which refer to or summarize the above-mentioned Croatian documents and positions […] . […] The Presidency proposes that this letter and the reply of the Republic of Croatia form an integral part of the accession documents (AD) of the Conference on the Accession to the European Union with Croatia.

With regard to the letter of the Presidency […] of xx December 2008, I hereby confirm that the government of […] Croatia fully agrees to the contents of the said letter and acknowledges its principles. This is on the understanding that the accession negotiations between the EU and Croatia will not in any way have any affect upon the final resolution of the border issue between Slovenia and Croatia and the position of both sides, in any procedure relating to the resolution of the border issue.

Croatia further notes that the second and third paragraph of the above-mentioned letter may not be interpreted, in the context of any procedure relating to the settlement of the border issue between Slovenia and Croatia, as implying on the part of any Member State of the EU any acceptance or rejection of Croatian statements and documents related to the border issue when made, produced or referred to in a context other than the accession negotiations between the EU and Croatia.

Croatia remains committed to resolving any border dispute in conformity with the principle of peaceful settlement of disputes in accordance with the United Nations Charter and in the spirit of good neighbourly relations [and] agrees to your proposal that your letter and this reply form an integral part of the accession documents (AD) of the Conference on the Accession to the European Union with Croatia. (Presidency Proposal, 15 December 2008: 1-2) The above letter and the positive reply of Croatia were supposed to function "as a disclaimer" and be part of the accession documents. The rationale behind this exercise was that the border dispute was a bilateral issue which was in no way related to the acquis, i.e. the substantive pieces of EU legislation touched upon in the actual negotiating Chapters, and that the EU was not going to enter into solving the border problem. However, substantial pressure from the Slovenian capital to start the solving of the border dispute was felt in the trilateral meetings, since (i) it was a very sensitive issue for the country anyway, and (ii) polling day in Slovenia was very close (interview civil servant involved in the trilateral meetings, 27-01-2017).

The Slovenian side was dissatisfied with the time-pressure as the French Presidency appeared to "rush it through" before the end of their term (31 December 2008). A solution may perhaps have been in the pipeline had more time been allocated to the drafting of the letters (interview senior Slovenian civil servant, 24-01-2017). On a more fundamental note, Croatia should even have had its accession documents modified to meet Slovenia's concerns (interview senior Slovenian civil servant 17-10-2016). In the end, Slovenia would not accept the Presidency proposal, and it was already becoming apparent that EU Enlargement Commissioner Olli Rehn was aiming at decontaminating the Croatian accession negotiations from the veto before the end of his own term which was to expire on 31 October 2009.

As things had developed into a real deadlock, the European Commission started assuming a mediating role in January 2009. Olli Rehn, the then European Commissioner for Enlargement, was determined to "avoid a major new frozen conflict in the Western Balkans" and went on a sentiment-finding mission to Ljubljana and Zagreb on 28 January 2009. He met Prime Minister Borut Pahor and President Danilo Turk in Ljubljana over lunch, and Prime Minister Ivo Sanader and President Stipe Mesić in Zagreb for dinner. Whilst Rehn was facing a mix of rational concern and a very emotional stance towards the other country respectively, there was no enthusiasm for his idea of mediation (interview Olli Rehn, 09-10-2015; interview Rehn Cabinet member who was with him on that trip, 13-11-2015) . 44 Still, a subsequent first confidential draft dated 26 January 2009 was circulated to the parties outlining the basic elements of a mediation exercise by a Senior Experts Group (SEG):

• The SEG would be set up to resolve the bilateral border (at sea and at land) based on international law; it would consist of three personalities, one of them the chair; • The Expert Group would, after "consult[ing] the authorities in both countries" issue recommendations that Croatia and Slovenia were supposed to respect; • The SEG would make its recommendations before the end of 2009; • No document presented in the accession negotiations with Croatia would "commit any of the negotiating States on the border issue"; • The Slovenian reservations were supposed to be lifted as soon as the countries made a declaration on mandating the SEG (Basic elements for a joint statement on European facilitation on the border issue between Slovenia and Croatia, European Commission note, 26 January 2009).

The draft declaration as such went through at least three drafting stages between the end of January and mid-March 2009 (Bickl 2017: 18 ; see also Draft Joint Declaration, 20 February 2009). A Croatian proposal contained a specific reference to "the work of the two commissions established under the Bled Agreement [2007] " and that the "International Court of Justice was […] the forum to which the border dispute was to be submitted". There was also talk of both parties acknowledging "the rights and obligations that derive […] from the UN Convention on the Law of the Sea". Further, bilateral negotiations were foreseen "on granting each other concessions with regard to the navigation regime and fisheries, once the border is decided by […] the International Court of Justice" (Draft Joint Declaration, undated). The last European Commission draft from 10 March 2009 mentioned, for the first time, the date of 25 June 1991 (the day of the declarations of independence of both Slovenia and Croatia) "as the basis for a solution". Furthermore, the consent of both parliaments was mentioned in the context of both countries respecting the Senior Experts Group's recommendations (Draft Declaration on the border issue between the Republic of Slovenia and the Republic of Croatia, 10 March 2009).

A first fully fledged European Commission "Draft Agreement on Arbitration", albeit still with the Senior Experts Group as the third-party mediator, surfaced towards the end of March 2009. The Commission neatly describes the approach as "contain[ing] elements from mediation and conciliation" (European Commission, note to the file, 12 March 2009; see also Sect. 1.3.1.4) highlighting the fact that what the two parties were supposed to enter into was a legally binding international agreement subject to parliamentary ratification (European Commission, Further reflections on a formalized document, fax dated 24 March 2009).

The "Draft Agreement on Arbitration" contained the following core elements:

• The above Draft Agreement already contained distinct features of arbitration such as a five-member body including two party-appointed members, provisions on the task of the third-party dispute resolution body and the applicable law, the submission of documents and counter-documents (albeit not referred to as memorials), oral hearings, and a binding award. Further, the nexus between an arbitration agreement and the lifting of the Slovenian reservations thus unblocking the Croatian accession negotiations was already there, too.

Nevertheless, both Slovenia and Croatia were not fully warming to the idea of the Senior Expert Group mainly because both the task of the Group and the applicable law were not yet sufficiently outlined. 45 As a consequence, the phase for setting up a specific arbitral tribunal began (interview Olli Rehn, 09-10-2015) . The Commission had learnt that "a proper judicial procedure was indispensable for the Croats 46 ", whereas taking on board some kind of discretionary powers for the tribunal would be vital for the Slovenes. In the following weeks, the Commission drafted a proposal for an arbitration agreement modelled on established arbitral rules and practice and based on the specific definitions needed for the peculiarities of the Croatia-Slovenia case (interview Frank Hoffmeister, then European Commission Legal Service, 03-06-2016; see also PCA Final Award 2017: 33, para 107-8).

The first draft proposal for the later Arbitration Agreement, known as Rehn I, aiming at establishing and mandating an Arbitral Tribunal, was circulated to the parties on 23 April 2009. The gist of the core issues from the preceding proposal based on the Senior Expert Group (see Sect. 4.2.2.3) was retained, whereas the provisions on the task of the Tribunal and the applicable law were revised and defined in greater detail.

To do justice to the evolution of the core provisions of the Arbitration Agreement drafts it is worth quoting the main elements of Rehn I: [Preamble] The Government of the Republic of Slovenia and the Republic of Croatia (hereinafter referred to as "the Parties"), Whereas through numerous attempts the Parties have not resolved their territorial and maritime border dispute in the course of the past years, Recalling the peaceful means for the settlement of disputes enumerated in Article 33 of the UN-Charter, Affirming their commitment to a peaceful settlement of disputes, in the spirit of goodneighbourly relations, Welcoming the facilitation offered by the European Commission, Have agreed as follows: 45 Slovenia later expressly suggested that whilst agreeing "to settle this predominantly political dispute through adjudication" it had "consented to the primary proposal by Commissioner Rehn [for] the process of mediation" (Information on the amendments proposed by the Republic of Slovenia, 25 May 2009: 5). 46 In retrospect, Croatia referred to the Draft SEG Agreement from 24 March 2009 as "political arbitration" as opposed to "judicial settlement" in relation to the final Arbitration Agreement (Croatian Ministry of Foreign Affairs paper, September 2011: 8).

[…]

Article 2: Composition of the Arbitral Tribunal (1) Both parties shall appoint by common agreement the President of the Arbitral Tribunal and two members recognized for their competence in international law within fifteen days. In case that they cannot agree within this delay, the President and the two members of the Arbitral Tribunal shall be appointed by the President of the International Court of Justice.

(2) Each side shall appoint a further member of the Arbitral Tribunal within fifteen days after the appointments referred to in paragraph 1 have been finalised. In case that no appointment has been made within this delay, the respective member shall be appointed by the President of the Arbitral Tribunal.

(3) If, whether before or after the proceedings have begun, a vacancy should occur on account of death, incapacity or resignation of a member, it shall be filled in accordance with the procedure prescribed for the original appointment. (2) The Parties shall specify the details of the subject-matter of the dispute within one month after entry into force of this Agreement. If they fail to do so, the Arbitral Tribunal shall use submissions of the parties for the determination of the exact scope of the maritime and territorial disputes and claims between the parties.

(3) The Arbitral Tribunal shall render an award on the dispute.

(4) The Arbitral Award has the power to interpret the present Agreement.

(1) The Arbitral Tribunal shall apply (a) the rules and principles of international law for the determination referred to in Article 3 (1) (a) [emphasis added];

(b) international law, equity and the principle of good neighbourly relations in order to achieve a fair and just result for the determination referred to in Article 3 (1) (b) [emphasis added].

Article 5: Critical date No document or action undertaken unilaterally by either side after 25 June 1991 shall be accorded legal significance for the tasks of the Arbitral Tribunal or commit either side on the dispute and cannot, in any way, prejudge the award.

Article 6: Procedure

(1) Each side shall submit a memorial to the Arbitral Tribunal within two months after entry into force. Each side has the right to comment on the memorial of the other side within a deadline fixed by the Arbitral Tribunal.

(2) Unless envisaged otherwise, the Arbitral Tribunal shall conduct the proceedings according to the Permanent Court of Arbitration Optional Rules for Arbitrating Disputes between Two States.

(3) The Arbitral Tribunal may seek expert advice and organize oral hearings.

[…]

Article 7: The award of the Arbitral Tribunal (1) The Arbitral Tribunal shall strive to issue its award within one year after its establishment. The Arbitral Tribunal adopts the award by majority of its members […].

(2) The award shall be binding on the Parties and shall constitute a definitive settlement of the dispute.

(3) The Parties shall take all necessary steps to implement the award, including by revising national legislation, as necessary, within six months after the adoption of the award.

No document presented in the EU accession negotiations shall prejudice the Arbitral Tribunal when performing its tasks or commit either side on the dispute.

The above applies to all documents and positions either written or submitted orally, including, inter alia, maps, negotiating positions, legal acts and other documents in whatever form, produced, presented or referred to in the framework of the EU accession negotiations. It also applies to all EU documents and positions which refer to or summarize the above-mentioned documents and positions. 47

Article 9: The continuation of the EU accession negotiations according to the negotiating framework (1) The Republic of Slovenia shall lift its reservations as regards opening and closing of negotiation chapters where the obstacle is related to the dispute.

(2) Both parties shall refrain from any action or statement which might negatively affect the accession negotiations.

[…]

Article 11

(1) The present Agreement on Arbitration shall be ratified expeditiously by both sides in accordance with their respective constitutional requirements.

(2) It shall enter into force on the first day of the week following the exchange of diplomatic notes with which the parties express their consent to be bound. When looking at the revised core provisions of Rehn I (and its evolution in the subsequent proposals) with regard to (i) the task of the Tribunal (Article 3) and (ii) the applicable law (Article 4), it is crucial to recall that the difference between international law and equity, generally, is such that the judicial body possesses substantially wider discretionary powers under equity than if it exclusively applied international law (see Sect. 3.2.1). This distinction was the core legal issue of dispute during the negotiations around the Arbitration Agreement.

The practical implications of the two distinctive legal concepts may be seen as follows: the more leeway there is for the legal deliberations of the Tribunal, the greater the potential for maritime territorial decisions in favour of Slovenia compared to what it could expect under the strict application of international law, the latter obviously favouring Croatia's position. If we look at Articles 3 and 4 of Rehn I, it is apparent that both for the delimitation of the waters inside Piran Bay and for the territorial sea border outside the Bay, the provisions of the United Nations Convention on the Law of the Sea (UNCLOS 48 ) apply, whereas for the access of Slovenia to the high seas and the regime for the use of that access a wider set of legal and extra-legal (praeter legem) deliberations is available to the Tribunal.

Croatia approved of Rehn I on the understanding that it was presented to the parties on a "take-it-or-leave-it" basis (interview senior Croatian civil servant, 25-01-2017; see also Preamble 49 of the Sabor Decision on the Acceptance of the Draft Agreement on Dispute Settlement […] between Croatia and Slovenia, 8 May 2009). Zagreb's view was that it was of paramount importance that the delimitation of the land and maritime border between the two countries as referred to in Article 3(1)(a) was subject to international law exclusively. To that end, the additional equity and provisions relating to good-neighbourly relations for the regime of the maritime areas and the Slovenian access as in Article 3(1)(b) could, according to the Ministry of Foreign Affairs note, be tolerated, like it or not.

Notably, Croatia's green light did include the above-mentioned Sabor endorsement of the Draft Agreement signalling cross-party support. Rehn I was subsequently hailed by the domestic media as a national victory (internal note Ministry of Foreign Affairs Croatia 2012: 4) notwithstanding the fact that 3(1)(b) talked of territorial contact for Slovenia.

There was no vote in the Slovenian parliament. Instead, the government decided to send several amendments to Rehn I to the European Commission in mid-May 2009. Its main elements 50 are worth quoting and deserve a brief discussion. 48 Art. 15 UNCLOS stipulates that "where the coasts of two States are opposite or adjacent to each other, neither of the two States is entitled, failing agreement between them to the contrary, to extend its territorial sea beyond the median line every point of which is equidistant from the nearest points on the baselines from which the breadth of the territorial seas of each of the two States is measured. The above provision does not apply, however, where it is necessary by reason of historic title or other special circumstances to delimit the territorial seas of the two States in a way which is at variance therewith." This provision has, through case law, come to be referred to as the equidistance/special circumstances method (Tanaka 2015: 225-7; Rothwell and Stephens 2016: 427-36) . For a discussion on maritime delimitation, the provisions of UNCLOS, and the development of case law see Sect. 3.2. 49 "Taking into account that the proposed texts of the [arbitration] agreement […] were offered to the Republic of Croatia and the Republic of Slovenia on a take-it-or-leave-it-basis.". 50 Slovenia also introduced amendments to Article 2 (Composition of the Tribunal) asking to streamline the provisions on the appointment procedure with the PCA Optional Rules, and to Article 6 (Procedure) proposing to insert the possibility for the Tribunal to assist the parties in reaching an amicable bilateral settlement at any stage (Information on the amendments proposed by the Republic of Slovenia, 25 May 2009: 1-2; 5-6).

(1) The Arbitral Tribunal shall determine (a) the course of the maritime and land boundary between the Republic of Croatia and the Republic of Slovenia including Slovenia's territorial contact with the High Seas 51 ; and (b) the regime for the use of the relevant maritime areas. and Slovenia's contact to the High Sea.

In the Slovenian explanatory note, the amendment is labelled "crucial and […] therefore the most important point" suggesting that if the original wording of Rehn I was kept it would deny Slovenia the territorial contact ("the absolute red line") it had before 25 June 1991, i.e. in SFRY times. 52 It must be noted in that context that the access to the high seas, politically and historically, "is a symbol of freedom [for Slovenia] and carries the notion of real independence for the State" (interview senior Slovenian civil servant, 17-10-2016; see also Petrič 2017: 362). Further, mere "contact" would carry the meaning of access to the High Seas which all States were entitled to anyway under UNCLOS (Information on the amendments proposed by the Republic of Slovenia, 25 May 2009: 3). The note goes on to cite examples from maritime delimitation case law and treaties in support of the term "territorial contact" 53 and concludes that, on Article 3, the incorporation of "territorial contact" with the High Seas was necessary "to ensure that [Slovenia's] vital interest is decided upon by the Arbitral Tribunal" (Information on the amendments proposed by the Republic of Slovenia, 25 May 2009: 4).

With regard to Article 4 (Applicable Law) the amendment reads:

(1) The Arbitral Tribunal shall apply (a) the rules and principles of international law for the determination referred to in Article 3 (1) (a);

(b) international law, equity and the principle of good neighbourly relations, taking into account also vital interests of both Parties and all relevant circumstances, in order to achieve a fair and just result; for the determination referred to in Article 3 (1) (b). and should therefore decide ex aequo et bono.

In the explanatory note, the original wording of Rehn I in relation to Article 4 ("international law" for the determination of the land border; "international law, equity and good-neighbourly relations to achieve a fair and just result" for the regime and the contact to the high seas) is critiqued for following "the Croatian demand that the border is settled through the strict application of international law" and for the 51 approach that "the resolution of the border issue would […] be distinguished from the resolution of the issue of [the] Slovenian more liberal regime through, presumably, Croatian territorial waters". The Tribunal should instead apply "the same principles to the entire dispute" (Information on the amendments proposed by the Republic of Slovenia, 25 May 2009: 4).

The application of the principle ex aequo et bono was "crucial due to the very special circumstances of the dissolution of the former SFRY", and "the true meaning of the ex aequo et bono principle is in fact to offer the parties a possibility to widen the margin for decision-making and to give the Arbitral Tribunal a discretionary power to find, outside the strict legal prescription, the basis for a satisfactory solution, when it considers that strict law would lead to unjust decisions (summum ius, summa inuria)". It would be clear, however, that ex aequo et bono was meant as an add-on tool for the Tribunal "if it finds the law to be either defective or incomplete, [so] that it could base itself on extra-legal consideration[s]" (Information on the amendments proposed by the Republic of Slovenia, 25 May 2009: 5). 54 The Slovenian note goes on to highlight the reference to "vital interests" and "relevant circumstances" as "draw[ing the Tribunal's] attention to the need to evaluate the effect of the important economic role of the Port of Koper, historic facts, exercise of fishing rights and other circumstances" (Information on the amendments proposed by the Republic of Slovenia, 25 May 2009: 5).

In relation to Article 9 (continuation of the EU accession negotiations according to the negotiating framework) Slovenia proposed the following:

Article 9: The continuation of the EU accession negotiations according to the negotiating framework

(1) The Republic of Slovenia shall lift its reservations as regards opening and closing of negotiation chapters where the obstacle is related to the dispute after the entry into force of the present Agreement.

(2) Both parties shall refrain from any action or statement which might negatively affect the accession negotiations.

Slovenia argues that since the Agreement would only be legally binding after its ratification by both parliaments and the exchange of diplomatic notes confirming the accomplishment of that task [Article 11(2)], it would only be logical that the provisions of Article 9 could only apply as from the entry into force of the Agreement as a whole. "Consequently, Slovenia can properly protect its vital interests against Croatia's prejudices only with a valid agreement establishing a mechanism which would start the resolution of the border issue as well as annul the legal effect of the prejudices which were introduced into the EU accession negotiations by the Republic of Croatia". The deletion of the second paragraph was necessary because it implied that "the parties do not act in good faith", and that the provision could be interpreted as acting as an impediment "to participate constructively during Croatian accession negotiations" (Information on the amendments proposed by the Republic of Slovenia, 25 May 2009: 7-8).

In summary, the Slovenian amendments to Rehn I touch on core elements of the Commission draft, such as the task of the tribunal, the applicable law, and the timeline for the lifting of the Slovenian veto of the Croatian accession negotiations. With regard to the substantive points, the amendments seek to (i) safeguard a territorial link between Slovenian territorial waters and the high seas, (ii) enshrine such contact as the country's vital interest listing the special historic circumstances (inter alia the territorial contact Slovenia enjoyed during SFRY times), (iii) considerably widen the scope of the deliberations of the Tribunal by adding the principle of ex aequo et bono providing a set of extra-legal considerations (political, historic and economic), and (iv) reserve the right to maintain the reservations vis-à-vis Croatia until the entry into force of the Arbitration Agreement.

The European Commission presented a new proposal on 15 June 2009. The changes concern the Preamble, Article 2 (Composition of the Arbitral Tribunal), Article 3 (Task of the Tribunal), Article 4 on the Applicable Law, Article 6 (Procedure), and Article 8 on EU accession negotiation documents, which read as follows and are discussed straight after the respective article. This change incorporates "vital interests" as one substantive point of the Slovenian amendment to Article 4, albeit in a new and very different environment. The Commission deliberately inserted "vital interests" in the Preamble to politicise it and render it a joint positive meaning for both Croatia and Slovenia. "It seemed appropriate to insert a 'diplomatic bow' of the EU vis-à-vis both parties" (interview Frank Hoffmeister, then European Commission Legal Service, 03-06-2016). This move may be seen as in contrast to the original meaning intended by Slovenia in the context of Article 4.

On a different note, one needs to see a Slovenian leitmotif during the processing of the border dispute in the context of the EU accession negotiations of Croatia: it is the notion of "quid pro quo" in the sense that Croatia receives EU membership in return for a link to the high seas for Slovenia. "There is clearly a double dimension here" (interview senior Slovenian civil servant, 17-10-2016; for quid pro quo in relation to the arbitration procedure as such see PCA Partial Award 2016: 28, para 115). The actual Arbitral Tribunal at a later stage noted, in more general terms and, for obvious reasons, without reference to the issue of contact to the high seas, that "a nexus was established between the settlement of the territorial and maritime dispute and the accession of Croatia to the European Union" (PCA Partial Award 2016: 55, para 220). Croatia, however, has never expressly accepted the notion of quid pro quo, but the fact appears to have been sinking in during the negotiations over the Arbitration Agreement that the arbitration procedure as such "was the price to pay" for EU membership (interview European Commission civil servant involved in the accession negotiations with Croatia, 07-01-2016).

Article 2: Composition of the Arbitral Tribunal

(1) Both parties shall appoint by common agreement the President of the Arbitral Tribunal and two members recognized for their competence in international law within fifteen days drawn from a list of candidates established by the President of / by the Member responsible for enlargement of the European Commission. In case that they cannot agree within this delay, the President and the two members of the Arbitral Tribunal shall be appointed by the President of the International Court of Justice from the list.

(2) Each side shall appoint a further member of the Arbitral Tribunal within fifteen days after the appointments referred to in paragraph 1 have been finalised. In case that no appointment has been made within this delay, the respective member shall be appointed by the President of the Arbitral Tribunal.

(3) If, whether before or after the proceedings have begun, a vacancy should occur on account of death, incapacity or resignation of a member, it shall be filled in accordance with the procedure prescribed for the original appointment. (Draft Agreement on Dispute Settlement, 15 June 2009: 1)

The above provision newly inserted by the Commission does not relate to any of the Slovenian amendments. It leaves the pre-selection of candidates for the Tribunal entirely to the Commission. This must be seen as an effort to retain some authority for the Commission over the selection process. "This provision limits the autonomy of the parties, and it was plain to see that they may perceive this as a tough move. It is crucial, however, that the Arbitration Agreement was more than a purely legal affair, and that it was something special after all" (interview Frank Hoffmeister, then European Commission Legal Service, 03-06-2016). There are two new elements in this core article here. First, the link between Slovenia's territorial waters and the high seas has become a separate point. This is of relevance for two reasons, (i) since a separate point carries more weight as compared to being included as the second item of another point (as was the case in Rehn I), and (ii) inserting an additional point establishes a clear sequence which the Tribunal has to follow in determining the border. Second, there is a new term ("junction") for the link between the Slovenian territorial waters and the high seas. Obviously, "junction" moves away from the previous term "contact" in Rehn I in so far as it denounces the physical connection between two marine areas whilst keeping the notion of them being interconnected in a certain way.

"Junction" appeared to be the right term to the Commission as "it is sufficiently neutral and unclear" to be acceptable to both sides. This view entails the notion that either side can interpret "junction" in a different way, i.e. as a normative term (Slovenia) or rather as a purely factual meaning (Croatia) of some kind of link (interview Frank Hoffmeister, then European Commission Legal Service, 03-06-2016). As to "junction", Slovenia holds that it was taken from the English translation On balance, it may be said with some accuracy that the Rehn II version of Article 3, whilst retaining its remarkable spirit of compromise, has shifted somewhat in favour of the Croatian position since the increased weight of the link between the Slovenian territorial waters and the high seas (through making it a separate point) appears to have been over-compensated by replacing "contact" (with a clear physical connotation) by the more neutral term "junction". The second core article now prima facie features an additional criterion of flexibility for the legal framework mandating the Tribunal. Point (b) clearly takes on board the second part of the Slovenian amendment to Article 4 of Rehn I. One could, however, see the "taking into account [of] all relevant circumstances" as a mere paraphrasing of, rather than a supplement to, the preceding provisions of (b) defining the applicable law for the Tribunal as "international law, equity and the principle of good neighbourly relations in order to achieve a fair and just result" as already implying the "taking into account [of] all relevant circumstances".

It is useful to look at the underlying approach of the Commission's wording of Article 3. When drafting the provisions on the applicable law, different legal frameworks (international law, equity 55 ) were twinned with more political considerations (good neighbourly relations). "With respect to the first issue [the maritime and land border; Art. 3(1)(a)], the applicable law would be restricted to international law, whereas the two other issues [Slovenia's junction (Art. 3(1)(b)), and the regime for the maritime areas (Art. 3(1)(c))] are to be decided in line with broader considerations" (European Commission internal note, undated). This approach was to "reflect the EU dimension and its political spirit" and the peculiarities of the bilateral case (interview Frank Hoffmeister, then European Commission Legal Service, 03-06-2016).

Article 6: Procedure

(1) Each side shall submit a memorial to the Arbitral Tribunal within two months after entry into force. Each side has the right to comment on the memorial of the other side within a deadline fixed by the Arbitral Tribunal.

(2) Unless envisaged otherwise, the Arbitral Tribunal shall conduct the proceedings according to the Permanent Court of Arbitration Optional Rules for Arbitrating Disputes between Two States.

(3) The Arbitral Tribunal may seek expert advice and organize oral hearings […] . This additional provision reflects the Slovenian amendment to Article 6 stating that, if the parties so wish, the Tribunal stands ready to facilitate a bilateral settlement of the dispute. This enables a bilaterally negotiated agreement ahead of the conclusion of the arbitration procedure, should both parties really wish to go back to that level. The wording of Art. 6(8) does not constitute any bias vis-à-vis any of the parties. Generally, going back into the bilateral mode opens up endless opportunities for any of the parties to delay the negotiations and/or to finally not sign or ratify a bilateral deal whereas the final award of an arbitral tribunal is considered binding.

No document presented in the EU accession negotiations unilaterally shall prejudice the Arbitral Tribunal when performing its tasks or commit either side on the dispute.

The above applies to all documents and positions either written or submitted orally, including, inter alia, maps, negotiating positions, legal acts and other documents in whatever form, produced, presented or referred to unilaterally in the framework of the EU accession negotiations. It also applies to all EU documents and positions which refer to or summarize the above-mentioned documents and positions (Draft Agreement on Dispute Settlement, 15 June 2009: 4)

The above insertion can be seen as mere clarification. The Commission made no further changes to the draft arbitration agreement.

Despite the fact that some of the amendments of the Commission could be seen as in favour of the Croatian position, in particular the new wording "junction" in 55 For the nature of equity and its role in maritime delimitation see Sect. 3.2.1.

Article 3(1)(b), but perhaps also the "vital interests" in the Preamble, Zagreb rejected Rehn II for reasons of principle. The Sabor had already accepted Rehn I which was considered a "grand step forward" as it had moved away from the SEG approach largely based on political criteria to a proper judicial procedure mainly based on international law (internal note Ministry of Foreign Affairs Croatia 2012: 3-4 

The Croatian Prime Minister Ivo Sanader unexpectedly resigned on 1 July 2009, largely on the grounds that he had not managed to lift the Slovenian veto and that, after all, the EU accession of Croatia had always meant a "life-time project" to him (interview Ivo Sanader, 19-05-2016) . Jadranka Kosor became the new Croatian Prime Minister. Bilateral relations appeared to have entered a new phase, mainly for two reasons:

First, the working atmosphere between Pahor and Sanader had always been perceived as difficult by both sides (interview Ivo Sanader, 02-11-2017; interview Borut Pahor, 20-06-2017) and there had been a fundamental disagreement between the two prime ministers on the nexus between EU enlargement and the resolution of the bilateral border dispute. Whilst Slovenia insisted on the quid pro quo approach. i.e. Croatia receives EU membership in return for the Slovenian junction to the high seas (interview senior Slovenian civil servant, 17-10-2016), Sanader had always fiercely rejected that package deal. Sanader's position was that the solution of the bilateral border dispute cannot be a precondition for Croatia as it was not one for Slovenia either by the time they joined the EU in the first place (interview Ivo Sanader, 02-11-2017 Second, there appears to have been a mutual sense of having to restore bilateral relations. Both parties felt they were damaging their reputation on the international stage and doing harm to their economies. Croatia was increasingly worried about "losing its European perspective" (internal note Ministry of Foreign Affairs Croatia 2012: 5), whereas Slovenia "felt awkward with the stalemate" over the border dispute (interview Frank Belfrage, State Secretary in the Foreign Ministry of Sweden in charge of the file at the time, 26-04-2017) . What contributed to a renewed spirit of bilateralism was the fact that the Swedish Presidency holding office in the second half of 2009 made it clear that it was now up to Croatia and Slovenia to find a solution (internal note Ministry of Foreign Affairs Croatia 2012: 5). However, the Swedish Presidency was happy to facilitate not least because it was in favour of EU enlargement anyway (interview Frank Belfrage, 26-04-2017).

In early July 2009, Pahor phoned his counterpart Kosor expressing his readiness to meet soon. During a subsequent exploratory visit of Kosor's advisor to Ljubljana, it became clear that Pahor was worried about a potential escalation of bilateral tensions on the face of the arrest of a Croatian war veteran by the Slovenian police at the Dobava rail border crossing on 11 July 2009. It turned out that the man was going to attempt to assassinate Pahor. The Slovenian Prime Minister assured Kosor's advisor that he had a friendly attitude towards Croatia, whilst Kosor let it be known that she was aiming to build bilateral relations based on mutual respect and a search for a winwin situation rather than continuing the win-lose approach (internal note Ministry of Foreign Affairs Croatia 2012: 6). Pahor's feeling was that the fact that Kosor was at the head of the Croatian government was a "golden opportunity" to finish off the Croatian accession negotiations (interview senior Slovenian civil servant, 24-01-2017).

It is vital to note that the essential point of the new bilateral approach was to aim at a reversal of the previous order of tackling the two main issues. Instead of solving the border issue first and subsequently lifting the veto, the new approach now was to remove the Slovenian reservations by clearing the potentially pre-judging aspects of the Croatian accession documents first to subsequently be able to agree on the terms of the arbitration agreement in a less heated atmosphere. "The timing and the sequencing proved very sensitive, but there emerged a common understanding that the eventual arbitral award had to be de-coupled from Croatia's accession negotiations, and that all this ought to be beneficially face-saving for both sides" (interview Frank Belfrage, 26-04-2017) .

The meeting between Kosor and Pahor took place on 31 July 2009 at Trakošćan Castle. There was a solid tête-à-tête where it became clear that Pahor and Kosor were on good terms. A joint understanding was developing that the issue of the border had to be solved at the prime minister level and that arbitration, whilst it would have been unimaginable to agree on it bilaterally in 2008, was now the best way forward (interview Borut Pahor, 20-06-2017) , and that "we were courageous enough to do it" (interview Jadranka Kosor, 07-06-2016) . 56 At the Trakošćan meeting, the following points were agreed on:

• the Slovenian reservations would be lifted as soon as the Croatian Prime Minister sent a letter to the Swedish Presidency clearing the issue of the allegedly prejudging Croatian accession documents; • the letter would be jointly drafted by a Silent Diplomacy Group 57 ;

• negotiations on the Arbitration Agreement would resume on the basis of Rehn II as soon as the Slovenian veto was lifted; • Croatia insisted on a statement on the Arbitration Agreement not pre-judging "territorial contact" of Slovenia with the high seas; and • the Arbitral Tribunal's award should be rendered after Croatia's accession to the EU (interview senior Slovenian civil servant, 24-01-2017; internal note Ministry of Foreign Affairs Croatia 2012: 5).

The drafting of the letter was supposed to be finished by the end of August. Against initial expectations, however, it was by no means a walk in the park given the still existing level of suspicion and sensitivities on either side. Nevertheless, the level of personal trust between the negotiators was constantly growing and it was crucial for the Swedish Presidency to feed the notion of "joint ownership" of an agreement on both the letter and the final Arbitration Agreement (interview Frank Belfrage, 26-04-2017) .

The basic challenge with the letter was that "we knew that Pahor was committed to the Trakošćan process, but would seek our assurances that Croatia will not walk away from the negotiations [on the Arbitration Agreement] once the blockage was lifted" (internal note Ministry of Foreign Affairs Croatia 2012: 8). What added to this difficulty of principle caused by the new sequence of tackling the two major issues was that Pahor was also under pressure domestically. Janez Janša, Pahor's predecessor and leader of the main opposition party SDS, wanted the border issue to be solved ahead of Croatian EU accession (interview senior Slovenian civil servant, 24-01-2017).

At the end of the day, the Slovenian Prime Minister consented to holding a meeting in Ljubljana on 11 September 2009 where the lifting of the Slovenian reservations and the re-start of the negotiations over the Arbitration Agreement should be made public. Subsequently, representatives of Pahor and Kosor went to see the Swedish Prime Minister Fredrik Reinfeldt in Stockholm to inform him of the upcoming Ljubljana meeting and the announcement about the veto being lifted and the resumption of the travaux préparatoires on the arbitration agreement. The texts of both (i) the 56 Jadranka Kosor did, however, share her predecessor Ivo Sanader's view to consider it "unfair that the border dispute was not an issue when Slovenia joined the EU" (interview Jadranka Kosor, 07-06-2016 Kosor letter clarifying the non-prejudging nature of the Croatian accession documents and the continuation of the negotiations on the Arbitration Agreement and (ii) Reinfeldt's reply were presented to him, including the new timetable for obtaining the arbitral tribunal's award after Croatia's accession to the EU. Reinfeldt welcomed the agreement, which turned into a major achievement of the Swedish Presidency (internal note Ministry of Foreign Affairs Croatia 2012: 8).

The letter was finally sent to Reinfeldt from Pahor's office minutes before the meeting of Pahor and Kosor in Ljubljana on 11 September 2009, which was considered "a major break-through" (interview senior Slovenian civil servant, 24-01-2017). The letter is worth quoting:

[W]ith the aim of addressing Slovenia's reservations on several negotiating chapters, on behalf of the Croatian Government, I would like to declare that no document in our accession negotiations with the European Union can prejudge the final resolution of the border dispute between Croatia and Slovenia. The above applies to all documents and positions either written or submitted orally, including, inter alia, maps, negotiating positions, legal acts and other documents in whatever form, produced, presented or referred to by the Republic of Croatia in the framework of the EU accession negotiations. It also applies to all EU documents and positions which refer to or summarize the above-mentioned documents and positions. 58

The resolution, or the way of resolution of the border dispute will be pursued through the continuation of the talks between Croatia and Slovenia facilitated by the European Union. It was also agreed that both sides will continue [the] negotiations on [the] border dispute settlement with the understanding either to submit the border dispute to the Arbitral Tribunal or to conclude [a] bilateral agreement on [the] common State border […] . Both sides also agreed that 25 June 1991 presents the basis for the resolution of the border dispute and that no document or action undertaken unilaterally by either side after that date shall be accorded legal significance for the tasks of any arbitral tribunal, or any other procedure relating to the settlement of the border dispute between Croatia and Slovenia, which will be entitled by Croatia and Slovenia to resolve the border dispute, and cannot, in any way, prejudge the outcome of the process.

Having in mind that we have properly addressed Slovenia's concerns related to the prejudices on the border between Croatia and Slovenia, we kindly invite the Swedish Presidency to convene an Inter-Governmental Conference in order to immediately resume Croatia's accession negotiations with the European Union. (Letter from Kosor to Reinfeldt, 11 September 2009) Reinfeldt's reply, sent three days later, was as follows:

The Swedish Presidency welcomes your letter, which properly addressed Slovenia's reservations on prejudices on the border between Croatia and Slovenia in negotiating chapters.

Having consulted the Republic of Slovenia and with the understanding that the guarantees given by the Republic of Croatia are sufficient for lifting its reservations on the opening and closing of the negotiating chapters related to Slovenia's reservations on prejudices on the border between Croatia and Slovenia, the Swedish Presidency will therefore convene on 2 October 2009 an Inter-Governmental Conference to resume Croatia's accession negotiations with the EU.

The Swedish Presidency takes note that both sides agreed to continue negotiations on the border dispute settlement, under the facilitation of the Presidency of the EU with the understanding either to submit the border dispute to the Arbitral Tribunal or to conclude [a] bilateral agreement on [the] common State border […] . The continuation of the negotiations between Croatia and Slovenia on the border dispute shall be convened simultaneously with the IGC.

It is understood that both letters present integral part of the accession documents of the IGC on Croatia's accession to the European Union. (Letter from Reinfeldt to Kosor, 15 September 2009) At the actual Ljubljana meeting on 11 September 2009, Kosor and Pahor managed to sustain their good terms despite the fierce respective domestic opposition to the compromise. They announced that the Slovenian reservations would now be officially lifted and that the talks over the Arbitration Agreement would resume.

Both issues materialised on 2 October 2009 when the respective negotiating Chapters with Croatia were opened or closed at an Intergovernmental Conference (IGC) in Brussels. On the sidelines of that IGC, a first trilateral meeting of the Croatian and Slovenian delegations with the Swedish foreign minister Carl Bildt plus Commissioner Rehn took place where Rehn II was on the table again. Participants did discuss a number of items based on a slightly amended Commission draft from 30 September 2009.

As for Article 2 (Composition of the Arbitral Tribunal), it was debated whether it should be the President of the European Commission or rather the Commissioner for Enlargement who would be in charge of drawing up the list of candidates. No agreement was reached. In the same vein, it was discussed whether the President of the International Court of Justice (ICJ) should be attributed the role of last instance in the appointment procedure, as set out in Rehn II. Again, no mutual consent could be reached. However, in relation to Article 6 (Procedure), the parties' preparation period for the memorials to be submitted to the Tribunal was extended from two to twelve months. 59 With regard to the timelines for the Tribunal (Article 7), the initial angle of the discussion centred around the deadline within which the Tribunal was to issue its award. To that end, the Commission had revised Rehn II as follows:

Article 7: The award of the Arbitral Tribunal

(1) The Arbitral Tribunal shall strive to issue its award expeditiously after due consideration of all relevant facts pertinent to the case within one year after its establishment. The Arbitral Tribunal adopts the award by majority of its members [...] . (Internal note European Commission, undated) This point was discussed in more detail at the 2 October 2009 meeting. There was a joint understanding that the aim of Article 7 was for the arbitral award to be delivered 59 It had become evident that the files could not possibly be prepared within a few weeks. Memorials tend to comprise not only the legal argumentaire, but also some detailed documentation of the history of the subject matter including archive material, such as maps or documents many of which had to be translated into English.

after the accession of Croatia to the EU. No agreement could be reached, however, on the wording. Croatia favoured "expeditiously" to be replaced by "within three years", Slovenia would accept a maximum of two years. 60 The issue was referred to a subsequent technical meeting the following week (European Commission internal note, undated). At the end of the day, it proved impossible to meet the ambitions expectations on the part of the Swedish foreign minister to arrive at a mutual consent on the full text of the Arbitration Agreement already during the 2 October meeting (internal note Ministry of Foreign Affairs Croatia 2012: 9).

As for the main facilitating third party in the final phase of the negotiations over the Arbitration Agreement, it must be noted that the subsequent phase was predominantly conducted on the bilateral level with the Swedish Presidency in a facilitating role.

Both parties considered the Swedish EU Presidency as a remarkably valuable facilitator in that respect. The Swedish diplomacy appeared well aware of the sensitivities of both Slovenia and Croatia and of the challenges ahead, played a very objective role, and was unanimously appreciated by both sides (interview senior Slovenian civil servant, 24-01-2017; interview senior Croatian civil servant, 25-01-2017). So was the effort and the role of Olli Rehn in the preceding months, who was perceived as acting with a sense of fairness and tact and with no secret agenda (interview Borut Pahor, 20-06-2017; interview Ivo Sanader, 19-05-2016) .

The European Commission obviously played a less active role after the breakdown of the talks over Rehn II (see Sect. 4.2.4), but was kept in the loop at all times (e.g. Swedish Ministry for Foreign Affairs fax to Olli Rehn, 25 September 2009; internal e-mail European Commission, 29 October 2009; interview Frank Belfrage, 26-04-2017) . As a new feature, Croatia and Slovenia, at the request of Zagreb, introduced the practice of also keeping the US diplomacy in the loop as a neutral witness (interview senior Slovenian civil servant, 24-01-2017; internal note Ministry of Foreign Affairs Croatia 2012: 10). 61 As for the remainder of the negotiations, there was mutual consent to start out from Rehn II as the basis (see Sect. 4.2.4), but not to touch on the previously hotly disputed Articles 3 (task of the Tribunal) and 4 (applicable law) any more (European Commission internal note, undated), and to finalise the Arbitration Agreement by November (interview senior Slovenian civil servant, 24-01-2017).

There were three outstanding issues to be tackled at a number of meetings taking place in turn in official residences in Croatia and Slovenia:

(i) the composition of the Arbitral Tribunal (Article 2); (ii) the non-prejudging issue of the Slovenian territorial contact; and 60 One must bear in mind that, in the autumn of 2009, the EU accession date for Croatia was not yet clear. In addition, the expectation at the time was that the Arbitration Agreement was going to be ratified and enter into force swiftly after its signature, i. It turned out that whereas the issue of non-prejudgement could only be resolved by a unilateral declaration 62 by the Sabor on the occasion of the Croatian ratification of the Arbitration Agreement, the two other issues had to be resolved in the text of the Agreement itself.

As for the composition of the Tribunal (Article 2), the question of who in the European Commission would be in charge of drawing up a list of candidates was solved through a compromise. Both the President and the Enlargement Commissioner were entrusted with that task. The President of the International Court of Justice (ICJ) was confirmed as the last instance of the appointment procedure to secure qualified judges as members for the Tribunal (internal e-mail European Commission, 29 October 2009).

With regard to the timelines, a new approach was chosen to safeguard the aim of delivering the award only after the accession of Croatia to the EU. Article 7(1) was left as it read in the most recent Commission draft ("The Arbitral Tribunal shall strive to issue its award expeditiously after due consideration of all relevant facts […]"; emphasis added). Instead, a new provision was inserted into Article 11. Croatia's initial position was that the Arbitration Agreement should enter into force on the day of Croatia's EU accession. Slovenia's initial stance was that the Arbitration Agreement should enter into force right after its ratification. The compromise formula agreed on in the end was that all timelines relating to the arbitration procedure would start on the day of signing Croatia's EU Accession Treaty (internal note Ministry of Foreign Affairs Croatia 2012: 11; interview senior Slovenian civil servant, 24-01-2017).

It must be noted, that the (technical) decoupling of the Croatian EU accession from the arbitration procedure as such was largely seen as the main "face-saving opportunity" for both parties (interview senior Croatian civil servant, 25-01-2017; interview senior Slovenian civil servant, 24-01-2017; interview Frank Belfrage, 26-04-2017). On the one hand, Slovenia was lifted of the burden of the role of holding Croatian EU accession hostage to the solution of the bilateral border issue, whilst at the same time receiving a binding Arbitration Agreement that incorporated the gist of Slovenia's vital interest in terms of mandating the Tribunal to create some form of link between the Slovenian territorial sea and the high seas. On the other hand, the obstacle for Croatia's EU accession was removed, Croatia's EU membership was virtually guaranteed, and the Arbitration Agreement provided for a proper judicial procedure where international law and the territorial integrity of Croatia played a strong role. 62 Croatia initially aimed at including the declaration on the non-predetermining issue of the Slovenian territorial contact in the actual Arbitration Agreement in some form. This was not acceptable to Slovenia, however, as it was regarded as a matter for the domestic Croatian ratification process. The US and Sweden were to witness the unilateral declaration (internal note Ministry of Foreign Affairs Croatia 2012: 7; European Commission internal note, undated; interview senior Slovenian civil servant, 24-01-2017).

The concluding agreement was reached on 26 October 2009 at a meeting between Kosor and Pahor in Zagreb (Hoffmeister 2012: 103) . The Arbitration Agreement (see Appendix A) was signed by the two prime ministers and witnessed by Reinfeldt on 4 November 2009 in Stockholm. It must be noted, however, that regardless of the high level of mutual personal trust within the bilateral Silent Diplomacy Group, the two parties were still somewhat "suspicious of one another" at the political level which manifested itself in last-minute phone-calls by the foreign ministers to the Swedish Presidency on the morning of 4 November, the day the Arbitration Agreement was to be signed (interview Frank Belfrage, 26-04-2017) Table 4 .1 provides an overview of the drafting stages of the Arbitration Agreement.

The signature of the Treaty of Accession of Croatia to the EU on 9 December 2011 66 triggered the timelines laid down in Article 11 of the Arbitration Agreement.

The first task to be accomplished was the composition of the Arbitral Tribunal pursuant to Article 2. To that end, the two Foreign Ministers, Samuel Žbogar (Slovenia) and Vesna Pusić (Croatia), came to Brussels for a trilateral meeting with the sitting EU Commissioner for Enlargement, Štefan Füle, in early January 2012. 63 The core element of the declaration reads: "Nothing in the Arbitration Agreement between the Government of the Republic of Croatia and the Government of the Republic of Slovenia shall be understood as Croatia's consent to Slovenia's claim to its territorial contact with the high seas" (Note verbale Ministry of Foreign and European Affairs of Croatia to the Embassy of Slovenia in Zagreb, No. 6257/09, 9 November 2009) . 64 In relation to the above declaration of Croatia, Slovenia insisted that "in accordance with international law the unilateral statement given with respect to the […] Arbitration Agreement cannot affect its substance and considers the Statement of the Republic of Croatia from 9 November 2009 as unacceptable and without any effect for the arbitral proceedings" (Note verbale of the Ministry of Foreign Affairs of Slovenia to the Embassy of Croatia in Ljubljana, No. ZMP 170/09, 21 November 2009 ; see also Petrič 2017: 365) . 65 The result was 51.5% in favour and 48.5% against with a turnout of 42.7% (Electoral Commission of Slovenia, 6 October 2010, see https://www.dvk-rs.si/index.php/si/arhiv-referendumi/refere ndum-o-zakonu-o-arbitraznem-sporazumu-6-junij-2010). 66 The Croatian accession treaty was signed by the EU Heads of State and Government, by the Croatian President and the Croatian Prime Minister at the European Council in Brussels (European Commission press release 9-12-2011; see https://europa.eu/rapid/press-release_MEMO-11-883_de.htm). The European Parliament had consented on 1 December 2011: https://www.europarl.europa.eu/sides/getDoc.do?pubRef=-//EP//TEXT+TA+P7-TA-2011-0538+0+DOC+XML+V0//EN&language=EN). Have agreed as follows:

Have agreed as follows:

Have agreed as follows:

Article 1: Establishment of the Arbitral Tribunal (2) Each side shall appoint a further member of the Arbitral Tribunal within fifteen days after the appointments referred to in paragraph 1 have been finalised. In case that no appointment has been made within this delay, the respective member shall be appointed by the President of the Arbitral Tribunal

(2) Each side shall appoint a further member of the Arbitral Tribunal within fifteen days after the appointments referred to in paragraph 1 have been finalised. In case that no appointment has been made within this delay, the respective member shall be appointed by the President of the Arbitral Tribunal

(2) Each side shall appoint a further member of the Arbitral Tribunal within fifteen days after the appointments referred to in paragraph 1 have been finalised. In case that no appointment has been made within this delay, the respective member shall be appointed by the President of the Arbitral Tribunal (continued) (3) The Arbitral Tribunal may seek expert advice and organize oral hearings (3) The Arbitral Tribunal may seek expert advice and organize oral hearings (3) The Arbitral Tribunal may seek expert advice and organize oral hearings (4) The Arbitral Tribunal shall, after consultation of the parties, decide expeditiously on all procedural matters by majority of its members (4) The Arbitral Tribunal shall, after consultation of the parties, decide expeditiously on all procedural matters by majority of its members (4) The Arbitral Tribunal shall, after consultation of the parties, decide expeditiously on all procedural matters by majority of its members (5) The proceedings are confidential and shall be conducted in English (5) The proceedings are confidential and shall be conducted in English (5) The proceedings are confidential and shall be conducted in English (6) The parties shall appoint representatives to act as intermediary between them and the Arbitral Tribunal. They may retain counsel to support their representative (6) The parties shall appoint representatives to act as intermediary between them and the Arbitral Tribunal. They may retain counsel to support their representative (6) The parties shall appoint representatives to act as intermediary between them and the Arbitral Tribunal. They may retain counsel to support their representative (continued) (2) Both parties shall refrain from any action or statement which might negatively affect the accession negotiations (2) Both parties shall refrain from any action or statement which might negatively affect the accession negotiations (2) Both parties shall refrain from any action or statement which might negatively affect the accession negotiations

Article 10: Stand-still

Article 10: Stand-still

Article 10: Stand-still

(1) Both parties refrain from any action or statement which might intensify the dispute or jeopardize the work of the Arbitral Tribunal (1) Both parties refrain from any action or statement which might intensify the dispute or jeopardize the work of the Arbitral Tribunal (1) Both parties refrain from any action or statement which might intensify the dispute or jeopardize the work of the Arbitral Tribunal

(2) The Arbitral Tribunal has the power to order, if it considers that circumstances so require, any provisional measures it deems necessary to preserve the stand-still (2) The Arbitral Tribunal has the power to order, if it considers that circumstances so require, any provisional measures it deems necessary to preserve the stand-still (2) The Arbitral Tribunal has the power to order, if it considers that circumstances so require, any provisional measures it deems necessary to preserve the stand-still

Article 11

Article 11

Article 11

(1) The present Agreement on Arbitration shall be ratified expeditiously by both sides in accordance with their respective constitutional requirements (1) The present Agreement on Arbitration shall be ratified expeditiously by both sides in accordance with their respective constitutional requirements (1) The Agreement shall be ratified expeditiously by both sides in accordance with their respective constitutional requirements

(2) It shall enter into force on the first day of the week following the exchange of diplomatic notes with which the parties express their consent to be bound (2) It shall enter into force on the first day of the week following the exchange of diplomatic notes with which the parties express their consent to be bound (2) The Agreement shall enter into force on the first day of the week following the exchange of diplomatic notes with which the parties express their consent to be bound (continued) 

At this moment, it is worth briefly recalling a few basic general features of arbitration and the origins of the Permanent Court of Arbitration (PCA). 

Arbitration can be seen as a most mature means of dispute settlement, and it dates back to 1794 when the UK and the USA, by means of the Jay Treaty, first formed panels of national experts appointed by the two States. The aim was to resolve a number of outstanding disputes between the two countries with regard to the border with Canada and claims of USA and UK citizens (Indlekofer 2013: 24-7; Bantekas 2015: 1-4) . Generally, arbitration tends to be used for subject matters that are of a legal nature, but need to be solved through a binding decision by a third-party judicial body, in this case an arbitral tribunal. The political aim often is to settle a dispute in order to improve or restore bilateral relations (Merrills 2014: 4; 2010: 568) 68 notwithstanding the fact that there are considerably more cases that are resolved by bilateral negotiations and diplomacy than through litigation by international courts or tribunals (Scott 2014: 24) .

One distinctive feature of arbitration is that the parties define the mandate of the arbitral tribunal, i.e. the questions the parties want the tribunal to answer and the criteria to be used to arrive at the final verdict. Thus, the mandate for the judicial body establishes both the scope of the arbitrators' jurisdiction and the applicable law (Tanaka 2018b: 116-118; Merrills 2014: 4-5) . It is vital to note that the parties can require that the arbitral tribunal apply specific rules on wider considerations other than international law (Tanaka 2018b: 106) . Scope and applicable law are one aspect of the parties exercising control over the process of arbitration.

Another feature of control over the process is that the parties nominate the arbitrators. This is usually done in two ways. First, the parties jointly agree on several members of the tribunal. Second, each party nominates one party-appointed arbitrator. It is of fundamental importance that, in so proceeding, the subject matter in question is considered to be going to be dealt with by a tribunal that commands the parties' trust (Tanaka 2018b: 106; Mourre 2010; Merrills 2010: 568) . It has become standard practice in State-to-State arbitration to have a Tribunal composed of three arbitrators and two party-appointed arbitrators, although three-or seven-member tribunals have also recently been in operation. 69 68 For territorial issues in particular, Brilmayer and Faure (2014: 195-6 ) posit three basic assumptions: (i) the uniqueness of territory (territory has a strong emotional component as people care about their homeland, and once territory is lost the grievance can last for several generations), (ii) judicial dispute settlement as a maximization strategy (if diplomacy is difficult and war is not on the cards, the acquisition of territory through third-party adjudication may be a viable alternative), (iii) avoidance of jurisdiction (territorial disputes are zero-sum by nature, so if one State can expect to gain, the other State will try to avoid adjudication). 69 Inter-State cases recently administered by or ongoing at the PCA at the time of writing include six five-member tribunals (Ukraine v. Russia, Italy v. India, Croatia v. Slovenia, Mauritius v. United Kingdom, Netherlands v. Russia, and Bangladesh v. India), two three-member tribunals (Malta v. São Tomé and Príncipe, Ecuador v. United States), and one seven-member tribunals (Pakistan v. India); see https://pca-cpa.org/en/cases/.

Fundamentally, arbitration plays a solid role in the dispute resolution toolbox of the United Nations Convention on the Law of the Sea (UNCLOS; see Sect. 3.2.2.1). 70 State-to-State arbitration does have its limitations, however. Negotiations in the diplomatic field account for a maximum degree of control over the process by the parties, whereas once the process of setting up an arbitral tribunal is over, so is direct control by the parties. A further weakness is that regardless of the task of arbitration to produce a binding settlement of a case, and unlike in commercial arbitration where the recognition and enforcement of foreign arbitral awards is considered truly global (Bantekas 2015: 223-7) , 71 enforcement in State-to-State arbitration cannot be guaranteed (Merrills 2010: 569) . 72 In a world of sovereign States, arbitration must rely "for its effectiveness on responsible behaviour from the parties" (Merrills 2014: 7) .

The Permanent Court of Arbitration (PCA) is the oldest existing dispute settlement body in the world. It was established in 1899 following the Hague Peace Conference the same year, which had adopted a Convention for the Peaceful Settlement of International Disputes. The Convention created the PCA, which subsequently enjoyed a first "Golden Age" until the creation of the Permanent Court of International Justice (PCIJ), the judicial institution of the League of Nations, in 1922 (Indlekofer 2013: 42-69) , and precursor to the International Court of Justice (ICJ) founded in 1945. Several reforms were carried out in the 1990s to render the PCA more attractive. The adoption of a number of optional rules and guidelines facilitated the use of arbitration (Tanaka 2018b: 109) and rendered arbitration a popular means of contemporary judicial dispute settlement.

Following the appointment of the members of the arbitral tribunal at the end of January 2012, the Tribunal held a first procedural meeting with the Parties on 13 April 2012. After a brief discussion of the procedural framework, the Arbitral Tribunal endorsed a proposal from the Parties for the following calendar for the pleadings: The Parties' first written memorials would be simultaneously submitted on 11 February 2013, and the Parties' counter-memorials were going to be submitted simultaneously 70 Inter-State-arbitration must be distinguished from investor-State (or mixed) arbitration between a State and an individual or a company, and, closely related, commercial arbitration between individual corporations. There are countless examples in the world of politics and business. For a contemporary and comprehensive survey see Moses (2017) . 71 Recognition and enforcement of awards in commercial arbitration are governed by the 1958 New York Convention which has been ratified by 157 States (as of 30 September 2018). For the Convention see https://www.uncitral.org/uncitral/de/uncitral_texts/arbitration/NYConvention. html. 72 Judgements of the International Court of Justice (ICJ), however, may be enforced by the UN Security Council (Scott 2014: 28) . Yet, such enforcement decision requires unanimity amongst its permanent members. on 11 November 2013. A hearing was scheduled for the spring of 2014 (PCA press release 13 April 2012; see also Article 6(1) of the Arbitration Agreement), and the Tribunal reserved the period from 26 May to 13 June 2014 for a hearing (PCA Final Award 2017: 48, para 153).

It must be noted that, pursuant to Article 6(5) of the Arbitration Agreement, the proceedings of the arbitration were confidential, so none of the submissions by the Parties are in the public domain except for the maps both Parties submitted for the purposes of the determination of the land border. 73 Therefore, any insight into the actual proceedings is somewhat limited to the official communication by the PCA and the Parties, and to pieces of information provided to the author by the Parties. In addition, some of the contents of the Parties' submissions is disclosed ex-post by "The Parties' Legal Arguments" in the Partial Award (PCA Partial Award 2016: 20-36, paras 87-140) and from "The Parties' Positions"/"Croatia's Position"/Slovenia's Position" throughout large parts of the Final Award (see PCA Final Award 2017: 69-359).

In the submissions of a judicial procedure, each of the Parties usually starts out with its so-called Requests where they state what they wish the Tribunal to adjudge and declare. In the following, the Requests of Croatia and Slovenia shall be summarised as for the maritime border. The land border requests will be neglected here as the corresponding maps were made public by the Tribunal with the consent of the Parties (see previous footnote).

With regard to maritime delimitation, Croatia, in its Memorial and Counter-Memorial, requested the Tribunal to adjudge and declare that (i) the delimitation in the Bay and of the territorial sea outside the Bay followed a simplified equidistance line starting from the mouth of the Dragonja (St. Odoric's Canal) to the sea border with Italy; (ii) the "Junction to the High Seas" under Article 3(1)(b) of the Arbitration Agreement did "not imply or allow any territorial contact between Slovenia and the High Seas"; (iii) pursuant to Article 3(1)(b) and (c) the Junction and the regime for the relevant maritime areas "shall be, mutatis mutandis, 

As for the maritime border, Slovenia requested the Tribunal to adjudge and declare that (i) the Bay "has the status of Slovenian internal waters and is closed by a straight baseline connecting the most prominent points on the coasts of the Madona and Savudrija promontories"; (ii) with regard to the territorial sea boundary, the border runs from Cape Savudrija in a west-southwest direction up to a point three miles from the Treaty of Osimo line and then, in a three-mile-distance parallel to the Osimo line further south west to a point 12 nautical miles off the Croatian coast south of Poreč [sic]; (iii) Slovenia's Junction to the high seas goes from the southern limits of its territorial sea to the Osimo line between Italy and the former SFRY; (iv) the regime for the use of the relevant maritime areas enables Slovenian fishermen to "enjoy their historical fishing rights in Croatia's territorial waters, which are also guaranteed by [Croatia's EU Accession Treaty] and the 1997 [SOPS] Agreement […]"; the corridor between Slovenia's territorial sea and the high seas constitutes high seas "within which Slovenia possesses sovereign rights over the continental shelf (sea bed and sub-soil)" (PCA Final Award 2017: 65-6, para 216).

Corresponding to (i) above, one Slovenian land border request needs to be mentioned here, namely the one running along the Croatian shores of Piran Bay, as Slovenia claims the Bay in its entirety. As a result, the land border, according to the Slovenian request, after reaching the Bay, "follows the coast of the Savudrija peninsula to the most prominent point of the Savudrija promontory […]" (PCA Final Award 2017: 63, para 214).

The hearing took place from 2 to 13 June 2014 at the PCA in The Hague, the Netherlands, where the Tribunal members put questions to the Parties to which they 

The Deputy Prime Minister and Minister of Foreign Affairs, Vesna Pusić, started off her country's pleadings by expressing the government's confidence in the arbitral proceedings and the importance the country and its people attached to the procedure (PCA press release, 17 June 2014: 1).

As for the applicable law, Croatia put an emphasis on Articles 3(1) and 4 of the Arbitration Agreement stressing that both the maritime and land border had to be determined first strictly applying the rules and principles of international law. Only after that boundary had so been determined could the Tribunal turn to items (b) and (c) of Article 3 regarding Slovenia's "junction to the high seas" and the "regime for the use of the relevant maritime areas". The determination of the two latter issues involved two further elements, equity and the principle of good-neighbourly relations. Croatia stressed that the two elements were to serve as a supplement to international law, not as a means to act in opposition to it. With regard to the land boundary, on the day of the critical date mentioned in the Arbitration Agreement, 25 June 1991, the republican boundary became the new international border between Croatia and Slovenia following the principle of uti possidetis juris. In practical terms, that meant that the outer limits of the respective cadastral units would define the border. To that end, Croatia urged Slovenia to give up the military post at Croatian Sveta Gera and to allow for unhindered travel between Sveti Martin na Muri and Murišće (PCA press release, 17 June 2014: 2).

In relation to maritime delimitation in particular, Croatia insisted that Article 15 of UNCLOS was the relevant rule of international law. It followed that the sea boundary, starting at the mouth of the Dragonja, had to follow the equidistance line through the Bay (which was not internal waters) and further up to the Osimo line, the sea border with Italy. According to Croatia, there were no special circumstances warranting a departure from the equidistance line (PCA press release, 17 June 2014: 2; see also Sect. 3.2.1).

With regard to the foreseen "junction", Croatia repeated its view that "junction" did not include the notion of territorial contact. As to the interpretation of "vital interests" mentioned in the Preamble of the Arbitration Agreement, they related to the Parties' commitment to the peaceful settlement of disputes. With regard to Croatia's vital interests in the negotiation of the Arbitration Agreement, they concerned (i) the country's territorial integrity, including its territorial sea, first of all, and (ii) EU membership (PCA Final Award 2017: 288, para 933; for maritime delimitation and Article 15 UNCLOS see also Sect. 3.2.1).

Further on the terms "junction", and "regime" (for the use of the maritime areas) referred to in Article 3(1)(b) and (c) of the Arbitration Agreement, Croatia stressed its position that they could not affect the course of the territorial sea boundary. Rather, these terms would be "limited exclusively to matters of maritime access and communications", i.e. the existing IMO Traffic Separation Scheme in the Northern Adriatic [PCA press release, 17 June 2014: 2-3; see also Section "Croatia's Requests" (iii)]. Croatia also noted that it had "legitimate interests" with regard to "security and defence concerns" and that the area south of the point where the Croatian territorial waters meet the sea border with Italy was not a relevant area in terms of the Arbitration Agreement and thus "excluded from any determinations by the Tribunal" (PCA press release, 17 June 2014: 3).

Slovenia's Agents introduced their country's pleadings referring to the Arbitration Agreement as a compromise respecting "the vital interests of both Slovenia and Croatia". The vital interest of Slovenia was the junction in terms of "direct geographical contact" to the high seas. That link was to be determined "by applying equity and the principle of good neighbourly relations in addition to international law" as stipulated in Article 4(b) of the Arbitration Agreement. The task of establishing such direct geographical contact was the conditio sine qua non for Slovenia's signing and ratifying of the Arbitration Agreement. Croatia's vital interest, according to Slovenia, was to become an EU member, a condition met by the time the Arbitration Agreement was adopted. Foreign Minister Karl Erjavec said the junction to the high seas was a "quid pro quo for the conclusion of the Arbitration Agreement", whilst the Slovenian Agent drew on the country's wider considerations in terms of security, navigation, historic and fishing rights, environmental protection, and the notion of the Slovenian identity of a European sea-faring nation (PCA press release, 17 June 2014: 3).

As for the land boundary, Slovenia called for the delimitation of the whole land border on the basis of legal title as of the critical date 25 June 1991. In the Mura River sector and the Central sector, delimitation based on existing historic legal title should be the rule, whereas in the Istria sector (including Snežnik and the lower Dragonja) the boundary should follow the cadastre as there was "no historic root of title". The Croatian reference to Slovenian activities on Trdinov Vrh/Sveta Gera and Sveti Martin na Muri was beyond the Tribunal's task, i.e. ultra vires (PCA press release, 17 June 2014: 4; for the history of Istria see also Sects. 2.2-2.4).

In relation to Piran Bay, Slovenia argued it was entirely internal waters of Slovenia as during SFRY times the Bay had been both a juridical and a historic bay. The status of the Bay "did not change after the dissolution of […] Yugoslavia" and therefore the principle of uti possidetis juris applied meaning it belonged to Slovenia which had "administered" the Bay from Piran for centuries (PCA press release, 17 June 2014: 4; see also Cataldi 2013: 7-8; for juridical bays see Sect. 3.1.1.2).

With regard to maritime delimitation, Slovenia addressed Article 15 UNCLOS (just as Croatia did) with an emphasis on the Article's second sentence covering special circumstances warranting a departure from the equidistance line. To that end, the Slovenia mentioned the "coastal concavity and the cut-off effect of the Istrian peninsula and Cape Savudrija", and the Slovenian continental shelf claim (PCA press release, 17 June 2014: 4).

The terms "maritime delimitation", "junction" and "regime", according to Slovenia, mentioned in Article 3(1)(a), (b) and (c) of the Arbitration Agreement, were three separate issues of one joint task the Tribunal was bound to fully comply with. As for the meaning of "junction" in particular, Slovenia argued that it would have to be "a line joining Slovenia's territorial sea to the high seas" which was an interpretation that covered both the term's ordinary meaning and "the drafting history of the Arbitration Agreement" whilst it was in line with "international law, equity and the principle of good neighbourly relations". Further, the existence of such junction would entail Slovenia not being separated from the high seas or any future economic zone.

Regarding to the regime for the use of the relevant maritime areas, Slovenia posited that the area south of the junction proposed by Slovenia, which was in line with UNCLOS, would remain high seas. That matter would go in line with Slovenia's continental shelf claim. Further, Slovenia stressed its "historic fishing rights in Croatia's territorial sea off the coast of Istria would be preserved" (PCA press release, 17 June 2014: 4).

The first time the Tribunal learnt of the fact that breaches of the confidentiality requirements of the arbitral proceedings 75 had possibly occurred was on 30 April 2015, by means of a Croatian letter including a note verbale (diplomatic note) to Slovenia dated 24 April 2015 (PCA Partial Award 2016: 12, para 67). 76 Foreign Minister Vesna Pusić expressed her government's concern vis-à-vis the Tribunal about two public statements of Slovenia's Foreign Minister from 7 January 2015 and 22 April 2015. The Croatian Foreign Minister also informed the President and the First Vice-President of the European Commission 77 as the Commission had facilitated the Arbitration Agreement in the first place. 75 Article 6(5) of the Arbitration Agreement reads: "The proceedings are confidential […]." Section 9.1 of the Terms of Appointment for the members of the arbitral tribunal stipulates that "[t]he Parties shall not engage in any oral or written communication with any member of the Arbitral Tribunal ex parte in connection with the subject matter of the arbitration or any procedural issues that are related to the proceedings" (Letter of the Tribunal to the Parties' Agents, 5 

The Croatian Minister's letter to the Tribunal quotes the Foreign Minister of Slovenia saying on the TV channel SLO 3 that he had talks in The Hague last year. And I made it very clear to the Arbitral Tribunal 78 that if they do not fulfil this task -we in Slovenia shall consider that the Arbitral Tribunal has not executed its mandate. Because the contact with the high seas has not been determined. With regard to another interview with the Slovenian TV on 22 April 2015, the Slovenian Foreign Minister is quoted as saying:

According to the information that I have, which is very much unofficial, as well as on the basis of a feeling that our legal team has, being composed of the world's best renowned scholars of the law of the sea, we are somehow optimistic in a way that the Arbitral Tribunal will determine that contact with the high seas. The Tribunal itself sent a letter to the Parties' Agents on 5 May 2015 79 stating that [t] he Tribunal is seriously concerned by the suggestion that one Party would have been privy to confidential information related to the Tribunal's deliberations. The Tribunal considers that such a meaning could be attributed to statements by the Slovenian Foreign Minister, and takes the view that such statements are unhelpful for the resolution of the present dispute […] .

In this regard, the Tribunal […] recalls the duty, incumbent on the arbitrators and the Parties' representatives alike […] that '[t]he Parties shall not engage in any oral or written communication with any member of the Arbitral Tribunal ex parte in connection with the subject 78 The Arbitral Tribunal asserts that "no private meeting between the Tribunal and Minister Erjavec occurred. The only occasions on which the Minister addressed the Tribunal were the hearings […] held at the Peace Palace in The Hague" (PCA Partial Award 2016: 12, footnote 8). 79 The letter was published on the PCA website on 20 June 2015 after the consent of both Parties. The official disclosure of any information relating to confidential arbitral proceedings can be regarded as exceptional. matter of the arbitration or any procedural issues that are related to the proceedings'. To the Tribunal, safeguarding the confidentiality of the deliberations until the issuance of an award is a matter of highest priority […] .

The Tribunal has also requested the PCA […] to review the processes that it has put in place to protect confidential information and has found these to be satisfactory […] The Tribunal is therefore confident that no information about the likely outcome of any aspect of the arbitration has been disclosed. (Letter of the Tribunal to the Parties' Agents, 5 May 2015: 1-2)

On 10 July 2015, the Tribunal informed the Parties that it "contemplates rendering the award in mid-December 2015" (PCA press release, 10 July 2015).

On 22 It is worth noting that no explanation had been provided as to the relation between the reported dates of the recordings and their publication, the source of the intercepted phone conversations, and how the recordings were handed on to the media (see PCA Partial Award 2016: 13-4, para 74).

Yet, at the beginning of April 2019, the Slovenian Prime Minister publicly announced that he had learnt from his intelligence service (SOVA) that the Croatian intelligence service (SOA) crafted the recordings (STA news, 4 April 2019). Further, it was revealed that a SOA operative was trying to prevent the Slovenian commercial TV station POP from breaking the news (STA news, 9 April 2019). The Foreign Ministry of Slovenia subsequently withdrew its Ambassador from Croatia for consultations (Foreign Affairs Ministry of Slovenia press release, 9 April 2019).

The matters touched upon in the recorded conversations mainly relate to (i) the arbitrators' preliminary views on contested issues, (ii) attempts to identify opportunities to influence Tribunal members, and (iii) documents received from the Slovenian Agent which the arbitrator appointed by Slovenia would submit to the arbitrators as his own. 80 https://www.mvep.hr/en/other/termination-of-the-arbitration-process; The website lists events between 30 April 2015, when the Tribunal was made aware of the statements of the foreign minister of Slovenia, and 25 June 2017, four days before the PCA Final Award. With regard to 22 July 2015, the Croatian Ministry has produced excerpts (translations from Slovene into English) of the published recorded conversations, see https://www.mvep.hr/files/file/dokumenti/arbitraza/en/150 820-excerpts-from-recordings-between-dr-sekolec-and-mr-drenik-14082015.pdf.

The following excerpts are taken from the PCA Partial Award and constitute certified translations commisioned by the PCA Registry. 81 (i) Arbitrators views on contested issues: Drenik: Maybe Vaughan Lowe. 82 Vaughan Lowe is more interested in these ecological issues, I think. Maybe he could… Sekolec: But he, he was quiet.

[…]

Drenik: This is typically French, if you ask me.… This is the same, the exact same mentality as Pellet, 83 he said to me 'knowing Guillaume' 84 he said to me. We will get the major part of the Gulf of Piran, we'll get the junction, but we will loss on Dragonja. We will lose on Dragonja [the speaker corrects herself]. Drenik: Excellent! You see, and you could just give him … 'I'm fine with that, I understand', you see, take-it-easy attitude … 'but look, I've checked this and here, I think that …' The point is not to give him 500 arguments, but just to say 'I still think it wasn't quite like this here.' Maybe he would then bring it up … Sekolec: Yes, yes.

Drenik: … because if it's you who does it [brings it up], Guillaume will wonder, but if Simma says 'I think we should nevertheless look into it a bit more …'.

Sekolec: I understand. I will … Drenik: Simma is certainly the one who knows best and the one who will delve into it.

Sekolec: Yes, I will work on Simma. This has been agreed already. The dinner. (Recording dated 11-01-2015; PCA Partial Award 2016: 14-5, para 77) (iii) Documents from the Slovenian Agent which the arbitrator appointed by Slovenia would submit as his own: Drenik: Well, you see, I could prepare all this for you, but there is something else. It would be a good thing to forward all these documents …. if you are going to forward them …. in such a way …. that you would bring your computer … Sekolec: Yes, so that I have the file.

Drenik: … and that we open a file in your computer and just transfer the documents, you know, the text. 81 For translated excerpts of the recordings in their entirety, see the Croatian Foreign Ministry website referred to in the last but one footnote above. Those transcripts, however, do not constitute certified translations commissioned by the PCA Registry. 82 Professor Vaughan Lowe was a Member of the Arbitral Tribunal. 83 Professor Alain Pellet worked as special advisor for Slovenia in the arbitral proceedings. 84 Judge Gilbert Guillaume was the President of the Arbitral Tribunal. 85 Judge Bruno Simma was a Member of the Arbitral Tribunal.

Drenik: This is very simple to do, you see, so that you are registered as the author of the file.

Sekolec: I understand, I understand yes, yes.

Drenik: Because otherwise, the text doesn't have an author and that would look strange and also, someone may break in and find it … if I am the author of the file. On 24 July, the day after the arbitrator appointed by Slovenia had resigned (PCA press release, 23 July 2015), the Croatian Foreign Minister sent a letter to the Tribunal indicating her government's "serious doubt [about] the integrity and fairness of the entire arbitration proceedings" in the light of the "shocking developments" (Letter from the Minister for Foreign and European Affairs to the Registrar of the Tribunal, 24 July 2015: 1). The letter went on to state that The conversations […] reveal that the most fundamental principles of procedural fairness, due process, impartiality and integrity of the arbitral process have been systematically and gravely violated, to the prejudice of Croatia. As you will be aware, the Terms of Appointment provide in Section 9.1 that 'the Parties shall not engage in any oral or written communication with any member of the Arbitral Tribunal ex parte in connection with the subject matter of the arbitration or any procedural issues that are related to the proceedings.'

[…]

[…] The communications appear to reveal that Arbitrator Sekolec inter alia disclosed critical elements of the Arbitral Tribunal's deliberations to Slovenia's Agent; advised her on the issues on which he believed the Tribunal was inclined to rule in Slovenia's favour, and on which issues it was not so inclined; requested […] arguments and 'facts' not already in the record so that he could use them in his discussions with other members of the Arbitral Tribunal as his own; conspired with Ms. Drenik to assure that the other members of the Tribunal would not know their true source; communicated these arguments and 'facts' to the other members of the Tribunal on the basis that they were his own.

[…]

[…] Croatia considers that the entire arbitral process has been tainted by the actions of Arbitrator Sekolec and Ms. Drenik […] Croatia has difficulty understanding how it would be possible, at this juncture, for the other Members of the Tribunal, or the PCA staff, to distinguish between the arguments and 'facts' presented by Slovenia through Arbitrator Sekolec, and those developed solely by Arbitrator Sekolec on his own. The official records appear to have been corrupted by improper argument and 'facts' submitted by one of the Parties after the close of the written proceedings and the hearings.

In these circumstances, Croatia asks the Tribunal to suspend the proceedings with immediate effect [and] to review the totality of the materials presented, and reflect on the grave damage that has been done to the integrity of the entire proceedings […] . (letter from the Minister for Foreign and European Affairs to the Registrar of the Tribunal, 24 July 2015: 1-2; emphasis added)

In a reply to a letter from the Tribunal from 25 July 2015 to Slovenia asking to provide any feedback on Croatia's letter, Slovenia, on 26 July 2015, responded informing the Tribunal of the resignation of Ms. Drenik, and conceded that "the conduct of one of the arbitrators and Slovenia's former Agent" had been "entirely inappropriate and intolerable" (PCA Partial Award 2016: 17, para 82; 42, paras 170-1; letter from the Republic of Slovenia to the Registrar of the Tribunal, 26 July 2015). Further, Slovenia opposed Croatia's view that the arbitral proceedings should be suspended (PCA Partial Award 2016: 17, para 83) positing that the Tribunal was still charged with fulfilling the task of settling the dispute that had been submitted to it (letter from the Republic of Slovenia to the Registrar of the Tribunal, 26 July 2015). On 28 July 2015, Slovenia appointed Ronny Abraham, President of the International Court of Justice (ICJ), as the new arbitrator to replace Jernej Sekolec (PCA Final Award 2017: 53, para 181).

In an extraordinary session on 29 July 2015, the Croatian Parliament (Sabor) unanimously "[put] the Government of the Republic of Croatia under an obligation to begin the procedure of termination of the Arbitration Agreement […] for reasons of material breach of its provisions by the Republic of Slovenia" (Sabor Resolution 29 July 2015). In a diplomatic note (note verbale) the following day, Croatia notified Slovenia that, pursuant to the Sabor Resolution, [t] he Republic of Croatia considers it is entitled to terminate the Arbitration Agreement […] In accordance with Article 60, paragraph 1 of the Vienna Convention on the Law of the Treaties, the Republic of Croatia considers that the Republic of Slovenia has engaged in one or more material breaches of the Arbitration Agreement. The Republic of Croatia hereby provides the notification pursuant to Article 65, paragraph 1 of the Vienna Convention that it proposes to terminate forthwith the Arbitration Agreement.

[…] As a result of the actions of […] Slovenia, the impartiality and integrity of the arbitral proceedings have been irrevocably damaged, giving rise to a manifest violation of the rights of Croatia.

The actions for which Slovenia is internationally responsible have violated inter alia Article 6 of the Arbitration Agreement, by violating the agreed procedure and rules of confidentiality and Article 10 of the Arbitration Agreement, which obliges the parties to 'refrain from any action or statement which might […] jeopardize the work of the Arbitral Tribunal'.

[…]

The principles of fairness and integrity have been violated, irreparable harm has been done to the legitimacy and prospects of the process. In the absence of any possibility that the arbitral process will now be seen to be fair and proper, and to meet all applicable standards, the object and purpose of the Arbitration Agreement cannot be accomplished. Croatia also informed the European Commission of the Sabor Ruling and the government's termination request (letter from the Minister for Foreign and European Affairs of Croatia to Frans Timmermans, Vice-President of the European Commission, 30 July 2015), and subsequently sent a letter to the Tribunal notifying the arbitration body that, as of 31 July 2015, Croatia terminates the Arbitration Agreement (and the arbitral proceedings as such) relieving Croatia's Agent, Co-Agent, Counsels and assistants "from their engagement in the case" (letter from the Ministry of Foreign and European Affairs of the Republic of Croatia to the Registrar of the Tribunal, 31 July 2015: 2).

The Croatian government took the view that "the Tribunal is without competence to express any views as to the requirements for the termination of the Arbitration Agreement" (letter from the Ministry of Foreign and European Affairs of the Republic of Croatia to the Registrar of the Tribunal, 31 July 2015: 2; emphasis added). For the Tribunal's deliberations on the legality of the Croatian termination request see "Legality of the Croatian Termination Request" in Sect. 4.3.4.3) . To that end, however, it must be mentioned that it is a well-established principle that an International Court or Tribunal can decide itself in matters of jurisdiction (compétence de la compétence or Kompetenz-Kompetenz); see e.g. Bantekas 2015 : 109-112, or the ICJ Nottebohm Case (ICJ Reports 1953 . In other words, "procedurally, Croatia was not on a strong footing with withdrawal" (interview Damir Arnaut, 25-01-2018) .

The Croatian move was not free of controversy in EU circles either. As the then chairman of the Foreign Affairs Committee in the European Parliament put it: "The Croats have organised their withdrawal from the arbitration procedure within a couple of hours, and they did it in the most brutal way possible. One has to acknowledge at the same time that they politically capitalised on the events in a professional way." (interview Elmar Brok, 15-11-2015) .

The arbitrator appointed by Croatia had resigned on 30 July 2015 on the grounds of the "gravity [of the] wrongful behaviour" of the former arbitrator appointed by Slovenia and the former Slovenian Agent (letter of resignation of Budislav Vukas, 30 July 2015) . The arbitrator newly appointed by Slovenia on 28 July 2015, the President of the ICJ, stepped down on 3 August 2015 on the grounds that "the current situation cannot meet [the] expectation […] to help restore confidence between the Parties and the Arbitral Tribunal and to allow the process to continue normally […]" (PCA press release, 5 August 2015). 87 87 Sands (2016: 897-8) argues that the quick resignation simply mirrors the fact that the appointment of the President of the ICJ was an "error" in the first place as the ICJ President acts as (last-resort) appointing authority in Article 2(1) of the Arbitration Agreement. For that reason, the appointing authority itself cannot possibly be appointed to the Tribunal. Philippe Sands was a member of the Croatian delegation in the arbitration procedure.

The two vacancies for the respective posts of party-appointed arbitrators remained unfilled by the Parties for the time being (Slovenia refrained from making a reappointment in order to "preserve the integrity [of the] ongoing proceedings", and Croatia had not made an appointment for reasons of principle due to its de facto withdrawal). On 25 September 2015, the President of the Tribunal appointed Rolf Einar Fife of Norway and Professor Nicolas Michel of Switzerland as new Members thus reconstituting the Tribunal (PCA press release, 25 September 2015; see also PCA Partial Award 2016: 7, para 49). 88 On the same occasion, the Tribunal already indicated that it would now consider the Parties' position with regard to "Croatia's stated intention to terminate the Arbitration Agreement and in respect of the possible implications for the present proceedings of the events reportedly underlying Croatia's decision", and that it "may invite further submissions from the Parties" (PCA press release, 25 September 2015).

The European Commission actively supported the Tribunal's decision to continue the proceedings. In a letter to Prime Minister Cerar and Prime Minister Milanović, Commission President Juncker and the First Vice-President Timmermans wrote:

We are pleased […] that the Panel […] has appointed two new members and is now again operational. While the setting of borders between Member States does not fall directly within the competences of the Union, the European Commission reiterates that open border conflicts between Member States shall be resolved promptly, not least because these can have an impact on the application of EU law. We, therefore, are confident that both Member States act in the spirit of sincere cooperation.

The Commission supports the continuation of the work of the Arbitration Tribunal. We trust that the arbitration process will provide for the appropriate mechanisms to deal with all issues that have arisen in full respect of the Arbitration Agreement, and that the parties will respect the decisions of the Tribunal. The Croatian government, however, noting the Tribunal persisted, made it clear that it had no intention whatsoever to come back to the arbitral proceedings, and it dismissed any relevance of the case with regard to the application of EU law. Prime Minister Zoran Milanović stated:

We are convinced that the Commission has no legal basis and thus should not be actively involved in this and a number of similar border disputes among numerous Member States. In this respect, I do not believe that any of these disputes has 'an impact on the application of EU law'.

The Croatian Government has initiated the procedure of withdrawal from the Arbitration Agreement following an unanimous vote in the Croatian Parliament. Thus, consequently, it has withdrawn from [the] arbitration proceedings, it shall not comment the possible intentions of the Tribunal, shall not participate in its work, and shall not consider itself obliged to receive and act upon any decisions the Tribunal may or may not reach.

We remain convinced that the only decision this ad-hoc Tribunal can reach to address the consequences of the actions of one of the Parties, while acting in accordance with the highest 88 The real motifs of the Croatian government will be difficult to explore. Still, one cannot neglect a general sense amongst the political elite in Croatia that arbitration was just another issue of external pressure. Fundamentally, during its first years after independence, Croatia had consumed territorial sovereignty largely on paper only. The UNPROFOR troops in the country from 1991-1998 are one issue, another being the EU requirement to collaborate with the ICTY (interview Dejan Jović, 02-11-2017) .

In a letter to the Parties from 1 December 2015, the Tribunal announced to hold a hearing on the legality of the Croatian termination request on 17 March 2016 setting deadlines for submissions. Annexed to the letter were two internal documents from Jernej Sekolec, the initial arbitrator appointed by Slovenia, on (i) "notes regarding the border on and around Dragonja", and (ii) "Mura River Sector: Various effectivités 89 by Slovenia". Whilst Croatia did not make any submission, Slovenia filed its written submission on 26 February 2016 (PCA Partial Award 2016: 8-9, paras 52-54; 57). The Parties took opposing views on whether the proceedings should continue. Their legal arguments centre around three items:

(i) the jurisdiction of the Tribunal, (ii) the obligation and/or ability to continue the proceedings, and (iii) the legality of the Croatian termination of the Arbitration Agreement.

Croatia did not appear at the hearing on 17 March 2016, nor had it filed any additional submissions prior to that hearing. The Tribunal, however, for the purpose of their deliberations, did take on board the positions from two Croatian letters to the Tribunal from 24 and 30 July 2015 (see Sect. 4.3.3.2) .

On (i) jurisdiction, Croatia contended that the Arbitration Agreement contained no provision as for disputes on the validity of the Arbitration Agreement, and that the Tribunal therefore had no competence on the matter of termination (PCA Partial Award 2016: 20, para 89).

With regard to (ii) the Tribunal's duty and ability to continue the proceedings, Croatia held that "essential procedural rules have been violated [and that] such violations cannot be remedied by the Tribunal" concluding that the arbitral proceedings had been "totally and irreversibly compromised" (PCA Partial Award 2016: 21-2, paras 90-94).

As for (iii) the legality of the termination request, Croatia claimed it was entitled to terminate the Arbitration Agreement as the ex parte communication on the part of Slovenia constituted a material breach of the Arbitration Agreement in such a way that the violations threatened the object and purpose 92 of the Arbitration Agreement in relation to Article 60 (3) (a) the other parties by unanimous agreement to suspend the operation of the treaty in whole or in part or to terminate it either: (i) in the relations between themselves and the defaulting State; or (ii) as between all the parties; (b) a party specially affected by the breach to invoke it as a ground for suspending the operation of the treaty in whole or in part in the relations between itself and the defaulting State; (c) any party other than the defaulting State to invoke the breach as a ground for suspending the operation of the treaty in whole or in part with respect to itself if the treaty is of such a character that a material breach of its provisions by one party radically changes the position of every party with respect to the further performance of its obligations under the treaty.

(a) a repudiation of the treaty not sanctioned by the present Convention; or (b) the violation of a provision essential to the accomplishment of the object or purpose of the treaty.

4. The foregoing paragraphs are without prejudice to any provision in the treaty applicable in the event of a breach.

In relation to (i) jurisdiction, Slovenia held that the Tribunal was competent to decide on the Croatian termination request referring to the well-established principle in international law named compétence de la compétence/Kompetenz-Kompetenz stipulating that an International Court or Tribunal can decide by itself in matters of jurisdiction (PCA Partial Award 2016: 24-27, paras 102-110; for the Kompetenz-Kompetenz power of arbitral tribunals see also e.g. Bantekas 2015: 109-112). On (ii) the Tribunal's duty and ability to continue the proceedings, Slovenia noted that the general duty and competence of the Tribunal had been set out in the Arbitration Agreement, and that the duty to settle the submitted dispute had been confirmed by many decisions of international courts and tribunals. Further, Croatia, having achieved its vital interest of becoming an EU member, was not to "be released from its commitment to arbitrate". Moreover, the Tribunal had "the possibility to redress the breach of confidentiality" 94 and that it had done so by replacing the party-appointed arbitrators, and by the de novo deliberations (PCA Partial Award 2016: 27-31, paras 111-123) .

With regard to (iii) the legality of the Croatian termination request, Slovenia argued that only "a gross infringement of an essential provision" of the Arbitration Agreement merited triggering Article 60(3)(b) of the Vienna Convention, i.e. entitling a party to terminating the obligation to arbitrate, which was not the case in the present circumstances. Therefore, according to Slovenia, the Tribunal did have "the means to accomplish the object and purpose of the Arbitration Agreement" (PCA Partial Award 2016: 34-36, paras 133-140).

On 30 June 2016, the Tribunal issued its Partial Award on the contested issue of whether the arbitral proceedings will continue. The Tribunal members unanimously decided that

• Slovenia had been in violation of the Arbitration Agreement, but the Arbitration Agreement as such remained in force. • Thus, the arbitration procedure would continue (Partial Award 2016: 57, para 231). Sect. 4.3.4 and Appendix B) . Further, the Tribunal noted that Croatia was provided with the Slovenian submissions and the transcripts of the 17 March 2016 hearing. In procedural terms, the Tribunal referred to the "well-established principle of international procedural law that a unilateral decision to withdraw from dispute settlement proceedings cannot bring such proceedings to a halt" and that this principle was also set out in the PCA Optional Rules. 95 Therefore, the Tribunal was in a position and under an obligation to carry on with the arbitral proceedings (PCA Partial Award 2016: 36, paras 141-143).

The Tribunal cited various court and arbitral decisions, 96 inter alia the ICTY Tadić case:

This power, known as the principle of 'Kompetenz-Kompetenz' in German, or 'compétence de la compétence' in French, is […] indeed a major part of the incidental or inherent jurisdiction of any judicial or arbitral tribunal, consisting of its 'jurisdiction to determine its own jurisdiction'. It is a necessary component in the exercise of the judicial function and does not need to be expressly provided for in the constitutive documents of those tribunals. The Tribunal concluded that, under general international law, an arbitral tribunal or judicial body had "the jurisdiction to determine its own jurisdiction" (PCA Partial Award 2016: 39, para 157).

As for the Arbitration Agreement and the Tribunal's jurisdiction to decide on the validity of the Croatian termination request, the Tribunal, amongst other things, quoted from the ICAO Council case of the ICJ:

[A] merely unilateral suspension per se [cannot] render jurisdictional clauses inoperative, since, one of their purposes [might be] to enable the validity of the suspension to be tested. If a mere allegation, as yet unestablished, that a treaty was no longer operative could be used to defeat its jurisdictional clauses, all such clauses would become potentially a dead letter, even in cases like the present, where one of the very questions at issue on the merits, and as yet undecided, is whether or not the treaty is operative -i.e. whether it has been validly 95 Article 28(2) and (3) of the PCA Optional Rules read: "2. If one of the parties, duly notified under these Rules, fails to appear at a hearing, without showing sufficient cause for such failure, the arbitral tribunal may proceed with the arbitration. 3. If one of the parties, duly invited to produce documentary evidence, fails to do so within the established period of time, without showing sufficient cause for such failure, the arbitral tribunal may make the award on the evidence before it". 96 terminated or suspended. The result would be that means of defeating jurisdictional clauses would never be wanting. (I.C.J. Reports 1972: 53-4, para 16) In conclusion, there was "no doubt that the Tribunal also has inherent jurisdiction to decide" whether the arbitral proceedings can continue (PCA Final Award 2016: 58, para 168).

The Tribunal noted that, by means of the ex parte communication (see Sect. 4.3.3 .2), the Agent of Slovenia and the arbitrator appointed by Slovenia "acted in blatant violation of [the confidentiality] provisions" (PCA Partial Award 2016: 43-4, para 175).

As for cases comparable to the present one, the Tribunal looked into Victor Pey Casado et al. v. Chile where one of the party-appointed arbitrators had provided that party with a draft decision from the Tribunal's deliberations. That arbitrator and a second one who had been challenged on different grounds resigned. Two new arbitrators were appointed, and, to ensure a level playing-field, the draft decision was communicated to the other party. 97 After a new hearing the then Tribunal rendered an award (PCA Partial Award 2016: 45-6, para 182).

The Tribunal subsequently explored whether the integrity of the proceedings in the Croatia-Slovenia case can be preserved, and, if so, in what way. It recalled that the Tribunal was recomposed properly with two new and independent Members following the resignation of the two party-appointed arbitrators (PCA Partial Award 2016: 46-7, para 183-6; see also Sect. 4.3.3.4) . In relation to the two documents the arbitrator appointed by Slovenia had introduced into the proceedings after the ex parte communication with Slovenia's Agent, the Tribunal found that the arbitrator had not presented any new arguments or facts that were not already in the official record of the Tribunal. 98 Besides, the views expressed by both party-appointed arbitrators visà-vis the arguments and facts on the Tribunal's record were of no relevance for the work of the Tribunal as they both had resigned, so procedural imbalance could not be observed, either. In conclusion, the Tribunal noted no obstacles as to the continuation of the arbitral proceedings (PCA Partial Award 2016: 48-9, paras 187-196) .

The Tribunal examined whether the actions of the arbitrator appointed by Slovenia and Slovenia's Agent constituted a material breach of the Arbitration Agreement by Slovenia which would entitle Croatia to terminate the Arbitration Agreement under Article 60(1) of the Vienna Convention (see Sect. 4.3.4.1) . It is important to note, 97 ICSID Case No. ARB/98/2, Award 08 May 2008, paras 34-43. 98 By late 2014, the Tribunal's Registry had prepared a list of both Parties' evidence of (i) legal title and (ii) effectivités of 142 pages (PCA Partial Award 2016: 47-8, para 190) . that the breach of the provisions under Article 60(3)(b) cannot be measured in terms of gravity or intensity, but that the crucial issue here is whether a breach is essential for the accomplishment of the treaty's, i.e. the Arbitration Agreement's object and purpose (see PCA Partial Award 2016: 53, para 215).

According to the Tribunal, the first object and purpose of the Arbitration Agreement was to secure Croatia's access to the EU, and that therefore "a nexus was established between the settlement of the territorial and maritime dispute and the [EU] accession of Croatia" (PCA Partial Award 2016: 54-5, para 220). The second object and purpose was "the settlement of the maritime and territorial dispute between the Parties", so that the "decisive question" was whether the breaches of the Arbitration Agreement's provisions by Slovenia rendered the very settlement of the border dispute unattainable (PCA Partial Award 2016: 55, para 222).

The Tribunal found that, by (i) communicating to the Parties the two documents that had been submitted by the arbitrator appointed by Slovenia in collaboration with Slovenia's Agent, (ii) demonstrating that the documents contained no new arguments or facts not already presented in the written or oral pleadings, and through (iii) recomposing the Tribunal to safeguard its independence and impartiality, 99 "the procedural balance between the Parties is secured" (PCA Partial Award 2016: 55, para 224). In conclusion, the Tribunal held that remedial action was taken so that breaches of the Arbitration Agreement by Slovenia did "not defeat the object and purpose of the Agreement" with regard to Article 60(1) of the Vienna Convention, and that therefore the Arbitration Agreement remained in force and the arbitration proceedings could continue (PCA Partial Award 2016: 55, para 225; emphasis added).

Whilst it would be difficult to challenge the jurisdiction of the Arbitral Tribunal arising from the well-established Kompetenz-Kompetenz principle (see Sect. 4.3.3 and Section "Jurisdiction"; interview Vladmir-Ðuro Degan, 21-11-2019), there have been alternative views as to both the continuation of the arbitral proceedings and the legality of the Croatian termination request.

In the aftermath of the publication of the ex parte communication, Sands (2016) felt that, notwithstanding the fact that he had acted as counsel for Croatia in the proceedings, "the centrality of the independence of the adjudicator" was at stake, and that the affair was going to cause "tremendous harm to the system of international arbitration both within and outside the PCA system" (2016: 898). On the way ahead, Savarian and Baker (2015) argued that it was legally and politically impossible to continue the arbitral proceedings since (i) it would be very difficult to enforce a final award under the circumstances of one party determined to withdraw from both the Arbitration Agreement and the arbitration process, and (ii) that, given the ex parte communication, there would be doubts about the award as such irrespective of its contents. Thus, the Tribunal itself should "terminate the proceedings citing grave procedural misconduct" to avoid "an unenforced and discredited award". Savarian (2016), ahead of the Partial Award, however, opined that Croatia was not entitled to terminate the Arbitration Agreement (as opposed to the arbitral proceedings as such), i.e. the quid-pro-quo nexus remained and "Croatia would either have to accept a re-start of the arbitration […] or […] have to agree with Slovenia on alternative means [such as ICJ or ITLOS] to settle the dispute".

With regard to the PCA Partial Award, Ilić (2017) contends, inter alia, that the object or purpose of the Arbitration Agreement was to be found in (i) Article 4(b) of the Agreement mandating the Tribunal to apply "international law, equity, and the principle of good neighbourly relations", 100 and in (ii) the PCA Optional Rules' provisions on arbitrator impartiality. 101 Therefore, according to Ilić, the Tribunal had "placed too much weight on finality as the main goal of arbitration" (2017: 373), and the nexus between the arbitration procedure and Croatian EU accession (see "Legality of the Croatian Termination Request" in Sect. 4.3.4.3) was "not as strong as the Tribunal described it" (2017: 374). In his view, the quid-pro-quo aspect of arbitration in terms of EU accession of Croatia could not contradict the purpose "to settle all disputes in an impartial and procedurally fair manner" which was why the ex parte communication could well be seen as a material breach under Article 60 of the Vienna Convention (2017: 375) thus entitling Croatia to terminate the proceedings. As to the replacement of the party-appointed arbitrators, Ilić holds that what was impossible to remedy is that the Slovenian side had learnt about the other arbitrators' viewpoints on certain facts or arguments (2017: 377) providing Slovenia with some "strategic insight […] as to how the Tribunal might in the future react to particular arguments" (2017: 382). In conclusion, the arbitral proceedings had been affected unfairly to the detriment of Croatia rendering the task of the Tribunal "impossible to fulfil" (2017: 382).

On 29 June 2017, one year after the Partial Award, the Tribunal issued the Final Award. The following sections will focus on the Tribunal's decision on the maritime 100 The author of this book, however, considers the provision in Article 4(b) of minor relevance in terms of object or purpose of the Arbitration Agreement, since the above article defines the Tribunal's toolbox of applicable law for the actual maritime delimitation stricto sensu (in particular the high seas corridor and the regime for the maritime areas in relation to Article 3 of the Arbitration Agreement labelled "task of the arbitral tribunal"; see also Sect. 4.2.4). 101 Article 15(1) PCA Optional Rules: "Subject to these Rules, the arbitral tribunal may conduct the arbitration in such manner as it considers appropriate, provided that the parties are treated with equality and that at any stage of the proceedings each party is given a full opportunity of presenting its case". border and areas. Nevertheless, the land border decision will be briefly addressed whilst a full land-border survey regrettably is beyond the scope of this study. 102

In its analysis with regard to the land border (as well as the maritime border), the Tribunal was bound to strictly apply international law as stipulated in Articles 3(1)(a) and 4(a) of the Arbitration Agreement (see Sect. 4.2.4) . It is worth noting in this context that, therefore, "the Tribunal is required to decide the matter from the legal, and not from the historical or political or sociological perspective. This is what the two [g]overnments have chosen and mandated" (PCA Final Award 2017: 108, para 335).

The approach of the Tribunal as for the delimitation of the land border was as follows: 102 For the Final Award see https://pcacases.com/web/sendAttach/2172; for the read-out video of the press conference (01:55) see https://files.pca-cpa.org/hr-sl/2017-06-29_VOD_V4.mp4. 103 It may be useful to note that the Tribunal approached the handling of effectivités with great caution: "[The] evaluation of effectivités is not a matter of counting or comparing instances of the exercise or display of authority à titre de souverain. Each instance-and the number of relevant instances put before an international tribunal in cases such as this tends to be low-must be examined in order to identify precisely what can properly be inferred from it. For example, a payment of taxes to an authority of State A and not of State B may evidence a belief that State A and no other State has authority over a particular place, or it may evidence no more than the fact that although both State A and State B maintained claims to the location in question, it was decided that the tax-payer should not (at least on that occasion) be required to pay twice. To take another example, the referral of a dispute to a particular court may be based upon the presence of the property in question or one or both of the litigating parties, or the making of a relevant legal instrument such as a will, within the jurisdiction of the court, or upon an agreement between the litigating parties. An exercise of sovereign authority with respect to facts or things at a particular location should not be assessed in isolation: it does not necessarily evidence the existence of exclusive sovereign authority at that location. The Tribunal has accordingly taken particular care to look for evidence that points clearly to the assertion of the public power of the State at the location in question, to the exclusion of the public power of other States. In doing so, it has been mindful of the fact that some activities, such as the levying of taxes, the organization of elections, conscription for military service, and law enforcement, are more likely to demonstrate the exercise of authority à titre de souverain than others, such as the delivery of mail or the provision of telephone or other services" (PCA Final Award 2017: 110-111, paras 342-3).

Further, it is important to note that there are "limits to the degree of detail" of any delimitation decision as for the later demarcation on the ground (PCA Final Award 2017: 113, para 354) for a number of reasons:

(i) The Tribunal had to work with the maps and verbal descriptions provided by the parties, so the precision of the decision may be seen as "inherently limited". As this makes it impossible to determine "every metre" of the land boundary, the parties will in any event need to deal with minor adjustments at the stage of demarcation (PCA Final Award 2017: 113, para 355); (ii) In its analysis, the Tribunal was limited to the submissions of the parties. It had been agreed on that the Tribunal would not carry out any independent on-site investigation themselves (PCA Final Award 2017: 114, para 356); (iii) There are cases where matters of convenience or practicality (such as avoiding meanders or enclaves) could not be considered, since the Tribunal was strictly bound to international law. This meant the parties may reach diverging practical arrangements for the course of the border on the ground (PCA Final Award 2017: 109, paras 337-9; 114, para 357; see also Petrič 2017: 367) .

With regard to the course of the land border, the Tribunal divided the boundary up into three sections: (I) Mura River Region, (II) Central Region, and (III) Istria Region. For illustration purposes, a tiny few prominent or noteworthy particular land border spots in the afore-mentioned regions must be addressed, such as (i) in the Mura river region (starting at the border tripoint Croatia-Slovenia-Hungary following the river downstream for about 25 km) where the border crosses the river many times-with all the impracticalities that entails for agriculture or river ferries, for example-a number of delimitations were made, 104 such as the Brezovec-del/Murišće hamlet which was determined to be Slovenian (PCA Final Award 2017: 131-6, paras 405-414); (ii) in the Haloze/Macelj area of the Central Region, a tiny forest strip of 0.5 ha which was not recorded in either of the border municipalities (sic) was delimitated according to a historic map from 1914 (PCA Final Award 2017: 163-4, paras 502-5); (iii) the peak of Sveta Gera/Trdinov Vrh, also in the Central Region, owing its significance to a television tower and a military facility constructed by the former Yugoslav Army and staffed by the Slovenian Army since October 1991 was delimitated to the effect that the border runs between the television tower 

It is useful to bear in mind that the Arbitral Tribunal was mandated to delimitate the maritime boundary and to decide on the maritime areas according to the Arbitration Agreement, i.e. The decisions will be outlined below followed by a brief discussion of scholarly views on the maritime aspects of the Final Award.

The Tribunal first determined the status of Piran Bay and concluded that, prior to the dissolution of the SFRY, the Bay had the status of juridical bay (see Sect. 3.1.1.2) and had been declared internal waters by Yugoslavia through the Coast Sea Acts from 1963 and 1987, and that the latter Act also defined the closing line of the Bay. That closing line was also included in a negotiating document from 1964 leading to the bilateral Osimo Treaty 1975 between Italy and Yugoslavia on the territorial sea border. The Tribunal thus decided that on 25 June 1991 the Bay was internal waters of Yugoslavia 107 closed by a line between the low-water marks of Cape Madona and Cape Savudrija (PCA Final Award 2017: 267-272, paras 862-885) .

As there are no UNCLOS provisions on the delimitation of internal waters, the Tribunal took the view that the delimitation in the Bay had to follow the same principles as the delimitation of a land boundary, notably the principle of uti possidetis (juris and effectivités). As there was no division of the Bay in SFRY times, neither a legal title inherited by any of the Parties, nor a condominium arrangement, delimitation was thus to be made on the basis of effectivités, i.e. claims of sovereignty based on factual control or administration of the area in question (PCA Final Award 2017: 273, paras 886-8) .

The Tribunal mainly looked at fishing activities and police patrolling in the Bay at the date of independence (25 June 1991). The arbitrators noted that the Slovenian fishing reserve was established in 1962 and managed throughout up until 1991, whereas the Croatian fishing reserve was created in 1976 without any follow-up management activity. The municipalities of Buje (Croatia) and Piran (Slovenia) did, however, get in touch in 1975 to co-ordinate the limits of the fishing reserves and reciprocal consent was sought and given in 1976 and 1978 respectively. This led the Tribunal to conclude that the fishing reserves covered the entire Bay eastward of the closing line, but that there was no express mutual recognition of the respective territorial extent of each of them (PCA Final Award 2017: 274-6, paras 891-901).

As for policing, the Tribunal noted that whilst the coast was controlled by the Yugoslav Navy stationed in Pula operating a radar facility at the Savudrija promontory, 108 at Republican level it was the police stations in Koper and Umag exercising the patrols to enforce safety regulations and the fight against illegal fishing and smuggling. The arbitrators found that Koper police station patrolled the Bay with two vessels supported by a radio link with the Savudrija Navy observatory, and that Umag police station was active mostly in the immediate vicinity of the Bay's Croatian shores (PCA Final Award 2017: 276-9, paras 902-913) .

In view of the above effectivités, the Tribunal decided that the delimitation line in the Bay was to be between the lines claimed by Croatia (equidistance) and Slovenia (entire Bay) expressly adopting the line from the bilateral Initialled Draft Agreement 2001 (Drnovšek-Račan Agreement; see Sect. 4.1.4). The said delimitation line meets the closing line of the Bay at a point "which is at a distance from Cape Madona that is three times the distance from that same point to Cape Savudrija" (PCA Final Award 2017: 279, para 912). As a result and in terms of surface, the Tribunal apportioned roughly four fifths of the Bay to Slovenia and one fifth to Croatia. 109

Ahead of its analysis of the Parties' arguments, the Tribunal started out by clarifying that it was bound to conduct a sequential analysis of the tasks it was mandated in Article 3(1) of the Arbitration Agreement, i.e. the Tribunal needed to determine the course of the land and maritime boundary first, followed by the determination of the Slovenian junction to the high seas, and lastly by a decision on the regime for the maritime areas. Practically, the Tribunal outlined to look at (i) the delimitation of the territorial sea between Croatia and Slovenia, (ii) the determination of the junction to the high seas, Slovenia's claim to a continental shelf, and to the regime for the maritime areas (PCA Final Award 2017: 292, paras 947-8).

It must be noted that the Parties had taken different views on the question of whether the Arbitration Agreement did foresee distinct steps of analysis. Croatia argued that the drafting history of the Arbitration Agreement (see clearly mirrored the fact that the issues territorial sea boundary, junction to the high seas, and regime for the maritime areas had been carefully kept apart on purpose. Slovenia, however, contended that the Tribunal had discretionary powers to decide the issues under Article 3(1) separately or together to arrive at a workable result (PCA Final Award 2017: 285-6, paras 922-5) .

Referring to the three-stage approach, 110 but in fact applying the two-stage approach for the delimitation of the territorial sea, the arbitral tribunal first drew a provisional equidistance line between the point where the delimitation line estab- Considering special circumstances which would warrant a departure from the provisional equidistance line, the Tribunal dismissed several of Slovenia's arguments notably the concave nature of the coast along the Gulf of Trieste, and the (short) length of the Slovenian coast in relation to the (very long) overall Croatian coastline. Slovenia had also claimed maritime entitlements it considers to have inherited from the SFRY. The Tribunal noted that the Yugoslav Republic of Slovenia enjoyed these maritime entitlements "as a matter of the SFRY law to share and participate in the uses of the maritime zones of the SFRY" and went on to state that [a]s a sovereign coastal State, Slovenia's entitlement is to the maritime zones generated by its own coastline alone, limited as that might be. It is very well established that international law cannot refashion nature by allocating to a State a maritime entitlement other than that generated by its own coastline. (PCA Final Award 2017 : 315, para 1006 The length of the coastal fronts of Slovenia and Croatia the Tribunal did not consider a special circumstance. No historic titles 111 had been established on the part of Slovenia either. The arbitrators did, however, consider the coastal configuration a special circumstance:

[T]he coastline of Croatia turns sharply southwards around Cape Savudrija, so that the Croatian basepoints [controlling] the equidistance line are located on a very small stretch of coast whose general (north-facing) direction is markedly different from the general (southwestfacing) direction of much the greater part of the Croatian coastline […] , and deflect the equidistance line very significantly towards the north, greatly exaggerating the 'boxed-in' nature of Slovenia's maritime zone. (PCA Final Award 2017: 319, para 1011; emphasis added)

The arbitrators thus modified the provisional equidistance line in a way to make sure that the delimitation line does "not disproportionately exacerbate Slovenia's boxed-in condition". This resulted in the final delimitation line of the territorial sea border between Slovenia and Croatia pointing slightly further southwest being approximately parallel to the first seaward stretch of the Slovenian-Italian territorial sea border starting out at San Bartolomeo Bay (PCA Final Award 2017: 321-2, para 1014; emphasis added).

The Tribunal first interpreted the term "junction" which was highly disputed between the Parties (see Sect. 4.2.4 ; see also PCA Final Award 2017: 324-331, paras 1016-1033). The arbitrators took the view that "the term 'junction' has an essentially spatial meaning and connotation" (PCA Final Award 2017: 342, para 1073) and determined that "'junction' signifies the physical location of a connection between two or more areas. In the present case, the Tribunal defined the term 'junction' as the connection between the territorial sea of Slovenia and an area beyond the territorial seas of Croatia and Italy" (PCA Final Award 2017: 344, para 1076).

As for the location of the Junction Area, the Tribunal decided that it be along the sea border between Croatia and Italy (Osimo border) inside Croatia's territorial sea with a width of 2.5 nm 112 running from Slovenia's territorial sea border with Croatia to the point where Croatian territorial sea meets the high seas (see Fig. 4 .4).

Slovenia had made a continental shelf (CS) claim overlapping with the Croatian CS and asked the Tribunal to delimitate the Parties' continental shelves on the grounds that a CS was to be subsumed under "relevant maritime areas" in article 3(1)(c) of the Arbitration Agreement.

The Tribunal determined in one single paragraph that the territorial sea boundary between Slovenia and Croatia established between the point on the closing line of Piran Bay and the Osimo border was an all-purpose boundary and that Slovenia thus "has no maritime zones extending west beyond that maritime boundary". Further, "Slovenia's claim to continental shelf rights is therefore incompatible with the Tribunal's determination of the entitlements of the two States in this area, and no question of continental shelf determination arises" (PCA Final Award 2017: 354, para 1103). Applying the mandate of Article 4(b) of the Arbitration Agreement ("international law, equity and the principle of good-neighbourly relations in order to achieve a fair and just result") as the applicable law, the Tribunal determined a regime which "is intended to guarantee both the integrity of Croatia's territorial sea and Slovenia's freedoms of communication between its territory and the high seas" (PCA Final Award 2017: 360, para 1123).

The freedoms of communication in the Junction Area are characterised as follows:

• Uninterrupted and uninterruptable access to and from Slovenia including its airspace; • Freedom of navigation and overflight, and the lying of submarine cables and pipelines; • All ships and aircraft of all States enjoy these freedoms irrespective of their nationality; • Passage is unconditional and cannot be suspended under any circumstances; • Submarine vessels have no duty to navigate on the surface 113 ;

• No exploring or exploiting of natural resources, i.e. no fishing or oil/gas exploitation.

The guarantees and limitations of the freedoms of communication in the Junction Area are:

• No boarding, arrest, detention or other interference of ships or aircraft by Croatia;

• Croatia cannot enforce its laws and regulations for ships and aircraft in the Junction Area 114 ; • Croatia may provide assistance to vessels when called upon including emergency situations (PCA Final Award 2017: 360-3, paras 1123-1136).

With regard to the "Duty of Cooperation and Other Agreements between the Parties" (emphasis added), the Tribunal, inter alia, raises the following main issues:

The Junction Area regime must be exercised with due regard also to the rights and obligations of other States. The Tribunal noted that "given the small size of the Junction Area and its proximity to adjacent States, this obligation is a particularly important element of the legal regime of the Junction Area" (PCA Final Award 2017: 362, para 1134; emphasis added).

Further, the arbitrators noted that the Award does not affect any existing or future agreements (on implementation, for example) between Croatia and Slovenia. In the same vein, the IMO Traffic Separation Scheme in the North Adriatic (with designated sea lanes for vessels going to and from the Gulf of Trieste and to/from the ports of Koper and Trieste) and international rules for air navigation, i.e. those of the International Civil Aviation Organization (ICAO), shall not be affected either. Similarly, the rights and obligations of Slovenia under EU law are not touched upon (PCA Final Award 2017: 363, paras 1136-7).

The maritime determinations of the Final Award have received a variety of scholarly responses which merits a brief discussion.

The Bay Bankes (2017: 3) notes that the Tribunal's decision stipulating that the legal status of Piran Bay remains internal waters, and is thus inherited from SFRY times, is consistent with the ICJ's 1992 judgement in the Gulf of Fonseca case (El Salvador/Honduras/Nicaragua) where the status of internal waters was confirmed for Otranto) does not include the freedom for submarine vessels to navigate under the surface (see e.g. Tanaka 2015: 109). 114 Ships and aircraft, however, must comply with Croatian laws and regulations, and Croatia can take enforcement action outside the Junction Area in accordance with international law. a pluri-national bay following decolonisation. Grbec (interview 10-07-2018) highlights that it was "a balanced and sound Award" and by confirming the Bay of Fonseca judgement the Tribunal had set a precedent for maritime issues in the post-Yugoslav region in the Adriatic. Further, this decision confirmed the principle of uti possidetis and that there was no automatic switch to territorial waters after independence. By delimitating using uti possidetis effectivités the Tribunal did not apply maritime law, but a principle otherwise used for delimitation on land. The 80-20 partition of the Bay, according to Grbec, pretty much reflected an informal agreement from February 1991 by the authorities on the ground for policing purposes which was applied at least up until the date of independence. 115 Insolia (2019: 228-229) notes that the Tribunal's reference to the Gulf of Fonseca case omitted a vital aspect for determining the status of the Bay, namely an agreement of the coastal States in terms of a consistent joint claim of the status of internal waters which the ICJ had emphasised in its 1992 judgement. This is to say that the ICJ focused most on the attitude of the successor States rather than merely assessing the status of the Bay at a time when it belonged to a single State. However, the Tribunal may have been restricted in their analysis by Article 5 of the Arbitration Agreement stipulating 25 June 1991 as the critical date meaning documents or actions after that date could not be considered. Degan (interview 21-11-2019) objects to the notion of internal waters: The Bay's status should have been determined as territorial sea and delimitated by means of the equidistance/special circumstances method.

There has been some criticism of the fact that the Tribunal made no determinations with regard to the use of Piran Bay. Cataldi (interview 18-07-2018) argues that a condominium approach would be a win-win situation with a particular regard to fisheries, as one would not have to worry about borders, referring to the 1983 agreement between Italy and Yugoslavia on a joint fishing zone in the Gulf of Trieste, whereby borders played a useful role when delimiting communities but not for the exploitation of resources. The Italy-Yugoslavia agreement is also mentioned by Insolia (2019: 231) who contends that, contemplating the 1992 Gulf of Fonseca judgement of the ICJ, State succession could well create condominium where a single undivided maritime area passes to successor States. The States were not bound to such regime indefinitely, as they may well agree on a delimitation bilaterally if they so wish. Further, condominium was a solution perfectly in line with Art. 123 UNCLOS stipulating that riparian States to a semi-enclosed sea are under an obligation to cooperate. 115 Slovenia holds that there were two meetings between the police authorities of both countries on 29 January and 26 February 1991 in Pula where that agreement had been reached. Croatia denies that such agreement was arrived at. The arbitral tribunal, however, could not take on board any of these arguments as there are no agreed records of the Pula meetings (PCA Final Award 2017: 278, para 909).

As for the Tribunal's decision to modify the provisional equidistance line for the maritime boundary recognizing the coastal configuration around Cape Savudrija as a special circumstance, Solomou (2017: 5) opines that the half-effect 116 given to the Cape and its coast was predictable and "in line with jurisprudence constante […] as established by a series of cases handled by the ICJ, ITLOS and arbitral tribunals alike". In the same vain, Grbec (interview 10-07-2018) takes the view that, generally, the Tribunal did not depart from settled jurisprudence.

Oude Elferink (2017), however is critical of the Tribunal's determinations, notably as for its treatment of Cape Savudrija as a special circumstance. First, in looking at the seaward projection of the southwest-facing part of the Croatian coastline south of Cape Savudrija, the Tribunal took "into account a part of the coast of Croatia that is not part of the relevant coast for the territorial sea delimitation" (2017: 6; emphasis added). According to Oude Elferink, "the limited maritime zone of Slovenia is not due to a notional cut-off effect resulting from the equidistance line […] , but the result of the limited dimensions of the Gulf of Trieste" with Slovenia being in a different geographical situation than Croatia "which faces the Adriatic proper beyond the Gulf of Trieste" (2017: 5-6). The treatment of the shape of Cape Savudrija in relation to the south-west facing direction of the remainder of the Croatian coast is also taken up by Insolia (2019: 233) . Whilst he acknowledges that the coast south-west of Cape Savudrija did not account for any base points for the construction of the equidistance line, this feature had been the only way for the Tribunal to take into consideration the unique geographical situation of Slovenia with its concave coast.

On the Junction Area and its regime, a task for the Arbitral Tribunal that required a "creative, innovative approach" (Petrič 2017: 371) , Grbec (interview 10-07-2018) posits that it was clear that the Tribunal could not take away any territorial sea from Croatia. With the solution of the Junction Area still being Croatian territorial sea, but with high-seas freedoms and absolute passage, the Tribunal had "reconciled the battle of principles in maritime delimitation" which constituted a highly interesting precedent. Bankes (2017: 4) considers the solution of the Tribunal "certainly elegant" in terms of offering Slovenia de facto high seas access, albeit without resource-related rights such as fishing or seabed exploitation, and keeping the limitation of Croatia's sovereignty in the Junction Area to a minimum. Much in the same vein, Insolia (2019: 233-234) considers the determinations of the Tribunal in respect of the Junction Area "creative and balanced" subjecting a part of the Croatian territorial sea to a functional regime guaranteeing the freedom of uninterrupted communication with an erga omnes character as in an EEZ whilst preserving the territorial sovereignty of Croatia.

Comparing the Junction Area with traditional instruments of transit passage or high-seas corridors, Ferri (2018) notes that the sui generis regime in the Junction Area provides for a number of novelties, in particular the complete exclusion of enforcement of domestic legislation on the part of Croatia in the Junction Area. In her view, an international straits regime with some corrective elements would have made for a fairer balance. In terms of precedent-setting value, the judgement constituted a strengthening of the claims of geographically disadvantaged States with regard to access to the high seas (2018: 671). Cataldi (interview 18-07-2018) posits that the Junction Area and its location are not free of controversy, mainly because it was not clear yet how Italy as the adjacent State should react. Italy was affected by that corridor solution, but not a party to the conflict. He goes on to question the need for a sui generis corridor for Slovenia altogether as innocent passage was a far-reaching principle where the riparian State hardly had any means to stop a ship in its territorial sea anyway. Scovazzi (interview 03-08-2018) holds that the Tribunal's decision on the Junction Area was well explained, and that the Junction Area was the crucial point for Slovenia outweighing by far the territorial sea delimitation. Yet, with regard to the regime inside the Junction Area, the fact that Croatia retained the right to adopt legislation, but was not going to be able to enforce domestic legislation in the Junction Area, was "strange".

This author submits that the Tribunal's decision on the Junction Area appears to be very much in line with the mandate from the Arbitration Agreement. Further, there is some precedent-setting value in terms of, first, interpreting the term "junction", notably a novel term in the jurisprudence of maritime delimitation, and, second, developing a regime for a junction corridor in the territorial sea of a State having to marry the principle of territorial sovereignty with the principle of freedom of navigation under the delicate circumstances arising from the Arbitration Agreement. Notwithstanding the Tribunal's express mention that the Final Award shall not affect other agreements, the Junction Area provisions nevertheless do have practical implications not least on the existing Traffic Separation Scheme in the Northern Adriatic; see Sect. 6.1.1.1.

It is not difficult to agree with Bankes (2017) that the Tribunal, on the whole, acted rather elegantly on the Junction Area. The precedent-setting value of the junction regime must not be underestimated in the post-Yugoslav context. There are pending maritime disputes, or provisional arrangements calling for a permanent solution, between Croatia and Montenegro, and between Croatia and Bosnia-Herzegovina, both in the context of the two countries' EU accession process. This issue will be addressed in more detail in Sects. 6.3.1 and 6.3.5.

With regard to the delimitation method for the territorial sea border (see Sect. 3.2.2.3), it may be observed that the Tribunal suggested that there is a uniform delimitation method for all maritime zones (territorial sea, EEZ, and continental shelf; PCA Final Award 2017: 311-312, paras 999-1000), whilst in Croatia v. Slovenia the Tribunal applied the two-stage approach. This calls for two comments: First, the Tribunal's express mention of the three-stage approach referring to its application by the ICJ's recent 2014 Peru v. Chile case (PCA Final Award 2017: 311, para 999) in contrast with the effective non-use of the test by the Tribunal itself in Croatia v. Slovenia creates some confusion as to the universal application of the three-stage approach and the need of the proportionality test generally. Second, this leaves the (dis)proportionality test-where no court or tribunal has ever managed to produce objective criteria in a scientific manner-ever more contested (see also Tanaka 2018a) . When every allowance is made for the fact that the proportionality test remains a sensitive issue, it would have been a good idea, for the sake of transparency, for the Tribunal to explain why it was not in a position to apply the test under the specific circumstances of Croatia v. Slovenia. It appears that, as regards delimitation of the territorial sea, simply no mathematical calculation is possible as no coastal lengths or other features in terms of relevant areas can be identified in the first place where a ratio with the maritime areas apportioned can be established.

There were a number of responses to the Final Award. For the analytical purposes of this study, it is useful to distinguish between the bilateral and the third-party level.

On the day the PCA Final Award was handed down, the Slovenian Prime Minister Miro Cerar said at a press conference in Ljubljana: In accordance with the arbitration ruling we will first call on the Republic of Croatia to pursue joint implementation. To this end, […] we will shortly […] be sending the Croatian side a formal call for dialogue regarding fulfillment and implementation of the ruling within a reasonable time frame […] .

I expect Croatia to respond to this and for us to be able to agree on joint further steps regarding implementation. We have six months to prepare for implementation of the ruling. And we will resolve any possible complications with our neighbouring country in an amicable and responsible manner, in accordance with the principle of observing good neighbourly relations. (Slovenian Prime Minister's Office press release, 29 June 2017) At a press conference in Zagreb on the same day, the Croatian prime minister Andrej Plenković said:

The first and most important message […] is that today's arbitration decision does not bind us in any way, nor are we thinking about applying its contents. The second message is that Croatia adopted its position on the arbitration very clearly and unambiguously in parliament two years ago today […] .

For us, this arbitration has no legal effect, but we remain willing for talks with Slovenia on resolving the outstanding border issue and we don't expect Slovenia to take any unilateral steps […] . Croatia, too, believes in peaceful ways of resolving disputes, including in arbitration, but only when it is clean, fair and in line with agreed rules. (Croatian Prime Minister's press release, 29 June 2017)

On 12 July 2017, Cerar and Plenković discussed the way forward in a 40-min têteà-tête meeting in Ljubljana, agreed to keep in touch on the border issue, not to raise tensions, refrain from any unilateral acts, and to continue the dialogue at their next meeting agreed to be held in Zagreb in September. In the second part of the meeting, the delegations were tasked with preparatory work for the Zagreb meeting on the border issue and all other open bilateral issues (interview Miro Cerar, 15-10-2018 , interview Andrej Plenković 28-06-2018 . There were also several other informal meetings of representatives of both sides. The intention was to create a bilateral document, which would outline the entire border and entail the provisions of the arbitration award (land, sea, maritime areas) without specifically citing the Final Award. The bilateral document would serve as the base document for the demarcation of the border. Ljubljana indicated some flexibility for necessary adjustments of the course of the land border whilst insisting on the Tribunal's decision regarding the maritime border and the Junction Area (interview senior Slovenian civil servant, 17-04-2020).

Whilst there appears to have been some sense of de-escalation at the above bilateral Ljubljana meeting, things soon re-escalated, however. At a Council meeting of the Organization for Economic Co-operation and Development (OECD) in Paris on 8 September, Slovenia and Hungary objected to Croatia's bid for OECD membership. Slovenia opposed the Croatian bid on the grounds that Zagreb was not implementing the arbitral award on the border (STA News, 8 September 2017) . 117 Further, on 15 September 2017, Slovenia filed a lawsuit against the European Commission for granting Croatia the derogation right to use "Teran" on wine labels of Croatian Istrian origin, "Teran" originally being a Slovenian Protected Designation of Origin (STA News, 15 September 2017; European Commission news, 19 May 2017) . The General Court of the EU dismissed the Slovenian action on 9 September 2020 (Judgement T-626/17).

On the sidelines of the UN General Assembly in New York on 19 September 2017, Plenković and Cerar agreed to hold the bilateral follow-up meeting in Zagreb on 27 September. Two days later, however, Plenković, in his speech before the UN referring to Slovenia's ex parte communication during the arbitration procedure, publicly accused Slovenia of "undermining the rule of law" (Address at the 72nd Session of the General Assembly, 21 September 2017: 6). 118 That statement came only a few hours after a bilateral meeting in a very good atmosphere. Cerar was "shocked" at Plenković's "impolite and unacceptable" wording, so that he cancelled his visit to Zagreb foreseen later that month (interview Miro Cerar, 15-10-2018) .

The atmosphere proved tense for some time, and after an exchange of letters in October, Cerar finally came to Zagreb on 19 December 2017. The border issue was the main topic, and Plenković had presented a draft paper to Cerar which aimed at the bilateral de facto implementation of main elements of the Final Award, but with a few adjustments.

It is worth quoting from the press conference with questions and answers. Miro Cerar, the Prime Minister of Slovenia, said: I came to Zagreb today primarily with the intention of discussing this issue that is important for both countries, given that the deadline for the preparation of the arbitral award implementation expires very soon, on 29 December. 119 I understand the standpoint presented by my colleague, Mr Plenković that the arbitral award is not binding for Croatia, although I cannot agree with it, personally and as the Prime Minister of the Republic of Slovenia […] .

The only way forward for Slovenia is to respect the arbitral award and to implement it together […] The arbitral award is an indivisible whole and must be respected as such. It covers two different dimensions, one being the sea which the Arbitral Tribunal delineated by a very clear line that does not require any particular implementation arrangements. Naturally, the situation is different on the land border, which calls for a formation of a joint mixed committee that will carry out the demarcation, naturally within the framework of the arbitral award, considering that there are still some minor adjustments to be made […] Slovenia insists on the application of the arbitral award, to which we are obliged by international law, as well as European law, because we are also aware of the European aspect of the award. (Government of the Republic of Croatia News press conference notes, 19 December 2017) Andrej Plenković, the Prime Minister of Croatia, said: 118 The Croatian prime minister said the following: "We believe that disputes should be resolved through peaceful means and in conformity with international law. It is of the utmost importance that all international adjudications meet the highest legal standards and fully respect their relevant rules. Compromising the impartiality or independence of international adjudicators and tribunals, as was the case in the terminated Arbitration Process between Croatia and Slovenia, makes their decisions legally void and left Croatia with no choice other than to withdraw from the arbitration process. We consider that this example of undermining the rule of law is a discouragement for States considering third-party dispute settlement" (Address UN General Assembly Session, 21 September 2017: 5-6; emphasis added). One must keep in mind that the Tribunal, in its Partial Award, found that (i) Slovenia did violate the Arbitration Agreement, but not to such extent that a termination would be justified, (ii) the files introduced by the arbitrator appointed by Slovenia contained no new facts which were not already there at the record of the written or oral pleadings, (iii) the Arbitration Agreement remained in force, and (iv) that the recomposed Tribunal's ability to render a Final Award impartially was unaffected (PCA Partial Award 2016: 36-58, paras 157-225; see also Sect. 4.3.4.3) . 119 There is an implementation deadline for the Final Award of six months laid down in Article 7(3) of the Arbitration Agreement. Thus, the expiry date for implementation was 29 December 2017; see Sect. 4.2.3.

In order for us to reach agreement from these two positions, we need to maintain discussions, reach an understanding on elements that are dividing us […] Our message is: the border, regardless of what it will look like in the end, needs to be set in a way that is acceptable to both countries and that it can be internally approved by both parliaments with the appropriate majority vote […] This requires a certain flexibility from both sides. (Government of the Republic of Croatia News press conference notes, 19 December 2017) Plenković referred to the draft legal framework he had handed over to his Slovenian counterpart on how to proceed with a bilateral solution. Croatia's aim was to agree on a protocol 120 regarding the state border which would include several key elements. One of them would concern the land border, another one the sea border, the third would concentrate on the navigation regime in Croatian waters [Junction Area] beyond the Bay of Savudrija, the fourth on forming a mixed [bilateral] committee which would address aspects of the identification and demarcation of the border, while the fifth would concern the manner in which such a document would be submitted to the parliaments of both countries and ratified in the end. (Government of the Republic of Croatia News press conference notes, 19 December 2017; emphasis and footnote added) Both sides apparently had a different understanding of where flexibility should apply. Fundamentally, however, it must be noted that whilst it is clear that any implementation of the decision of any judicial body on the course of the land border requires minor adjustments and demarcation on the ground, 121 sea border delimitations usually are absolute, fixed by the coordinates from the court/tribunal decision and require no fine-tuning, unless the parties agree to negotiate an alternative solution.

At the actual tête-à-tête part of the 19 December Zagreb meeting, Plenković had proposed to negotiate a bilateral agreement that would take the arbitration award as a starting point. His approach for the land border was that minor adjustments of the course of the land border could indeed be achieved during the demarcation stage. Yet, as regards the sea border, he mentioned to Cerar that he needed an adjustment of the delimitation line inside Piran Bay. "We wanted to see something closer to the equidistance line" than the partition determined by the Final Award, and that due to domestic pressure "I have no room for manoeuvre here" (interview Andrej Plenković, 28-06-2018) .

Cerar, however, firmly rejected the proposal to put aside the arbitration award and negotiate a bilateral agreement. "That approach was unacceptable to us. With the arbitration award we have something binding in our hands. Moreover, the border was in its entirety-on land and at sea-defined for the first time in the history of the two countries. Going down the bilateral path again, we would have the incalculable 120 A protocol is a bilateral agreement between governments which they undertake to apply, but which, unlike a treaty, is not subject to mandatory ratification. The Croatian prime minister later explained that the idea was that each government could decide whether it wishes to ratify the protocol (interview Andrej Plenković, 18-02-2018) . 121 It is standard practise to have a bilateral identification and demarcation body to remove impracticable features of the course of the border determined by an international court or tribunal, so that the border does not run through buildings, installations, or farmlands, for example (see also PCA Final Award 2017: 109, paras 337-9; 114, para 357). hurdle of ratification in Sabor." There had been not-so-fond memories in Slovenia of the 2001 Drnovšek-Račan deal the ratification of which failed in Croatia. "Why should we try that option again? You can have the most brilliant bilateral agreement on paper, but we would have no guarantees that it is actually going to be implemented" (interview Miro Cerar, 15-10-2018) .

The European Commission already made it clear at their meeting on 4 July 2017 that the arbitration ruling had some direct effect on the implementation of EU law, and that infringement proceedings may well be on the cards.

According to the minutes of the meeting, European Commission Vice President Timmermans said that although the Commission was not a party to the arbitration agreement, it had played a facilitating role in the process which led to the creation of an arbitration panel between Slovenia and Croatia. The Commission had unequivocally supported this arbitration process which should provide legal certainty in the interests of both parties and ensure the effective implementation of EU law […] . The Commission had clearly expressed the hope that both parties would respect the decision taken by the Arbitral Tribunal, thereby putting a definitive end to the border dispute between them. Although the award of the Arbitral Tribunal would not be directly binding on the Union as it was not a party to the agreement or the arbitral procedure […] it was likely that, in future, the European Court of Justice would be asked for a preliminary ruling on the award's effects on EU law.

Regardless of the substance of the award, the principle of international law that the decisions of an arbitral tribunal must be complied with and implemented was all the more important because it continued to be relevant in the context of territorial claims and border disputes […] . (minutes of the 2219th meeting of the Commission held in Strasburg, 4 July 2017: 20-1; emphasis added)

The Director-General of the European Commission's Legal Service reported that the arbitral award was the result of a valid international agreement entered into by Croatia and Slovenia and supported by the Union. The Commission had witnessed this agreement in the context of the accession negotiations with Croatia and had played a facilitating role in the appointment of arbitrators of the Arbitral Tribunal. In particular, the Accession Treaty of Croatia referred explicitly to the use of an arbitration procedure to settle the border dispute.

While the border between the two countries was a bilateral issue, it nonetheless had a direct effect on EU law, and therefore the Union had jurisdiction in respect of this matter. Pursuant to Article 17 of the Treaty on European Union, the Commission oversees the implementation of EU law under the control of the Court of Justice of the European Union. Lastly, EU caselaw left no room for doubt as to the obligation of the Union and the Member States to implement public international law, which it would be bound to demonstrate in this case. In conclusion, the Union could be requested to clarify the effects of the award on EU law in the event of infringement proceedings. (minutes of the 2219th meeting of the Commission held in Strasburg, 4 July 2017: 22-3; emphasis added) European Commission Vice President Timmermans said the day after that he "expects both parties to implement [the ruling]" (EC Daily News, 5 July 2017).

Several EU Member States and the US issued statements. The Benelux Prime Ministers stressed "the importance of the rule of law as the foundation upon which the EU is built […]" calling "on both sides to respect the arbitration award in a constructive spirit" (Joint Benelux Statement on Croatia-Slovenia arbitration award, 4 July 2017). A German Foreign Ministry statement had said that "[…] preserving the integrity of international courts and tribunals is in the common interest of all States. EU Member States must play an exemplary role in this" (German Foreign Ministry press release, 30 June 2017). The British Embassy in Zagreb, upon request, gave a statement to the Croatian media saying that the UK "support[ed] the Tribunal process [and] the lawful resolution of disputes", but that "the bilateral dispute was a matter for the Croatian and Slovenian Governments, which the UK wishes to see solved" and that "it is for the two parties to decide themselves how that is achieved" (UK Embassy Zagreb statement, 30 June 2017). The US Embassies in Ljubljana and Zagreb issued a statement saying "we are not taking sides in this dispute. It is up to [the] two countries, both EU members and NATO allies, to resolve this bilateral issue, and we are hopeful they can do so" (US Embassy in Slovenia Statement, 29 June 2017). 122 It is worth noting in this context that the entire Slovenian political and diplomatic elite had been engaged in "silent diplomacy" over the preceding months to highlight the importance of the arbitration ruling (interview Tanja Fajon, 22-11-2016 ; interview senior Slovenian civil servant, 10-07-2017).

The Slovenian government subsequently finalised preparations for a lawsuit before the Court of Justice of the European Union (CJEU) against Croatia for violations of EU law due to non-implementation of the 2017 Final Award.

It is useful to recall that there are two types of infringement procedures in the EU institutional set-up: proceedings (i) initiated by the European Commission against a Member State mostly on the grounds of insufficient or non-implementation of existing EU legislation (Article 258 TFEU), or those ( Art. 259 TFEU provides that an EU Member State must bring the complaint against another EU Member State before the Commission first. The Commission may or may not, within three months after the submission of the complaint, and after each of the parties concerned have submitted their position, issue an opinion and bring the matter before the CJEU. If the Commission does not produce an opinion, the Member State lodging the complaint may bring the matter before the Court directly after the expiry of the three-months deadline. 124 Slovenia The Commission shall deliver a reasoned opinion after each of the States concerned has been given the opportunity to submit its own case and its observations on the other party's case both orally and in writing.

If the Commission has not delivered an opinion within three months of the date on which the matter was brought before it, the absence of such opinion shall not prevent the matter from being brought before the Court. 125 In the event of proceedings before the CJEU at a later stage, the Commission may well present an opinion-and did so, on the Court's request regarding the issue of Croatian inadmissibility motion. Any Member State interested in making a submission to a CJEU file can do so, too. See Art. 196 Rules of Procedure CJEU. the binding nature of the Final Award, corresponds to the findings presented during the Commission College meeting of 4 July 2017 (see Sect. 4.3.6 .2) confirming that the border dispute was solved by means of the Final Award which was now part of international law the EU had to respect (Internal note European Commission, 14 May 2018: 3-4).

The Slovenian caretaker government 126 subsequently launched the Art. 259 lawsuit directly before the Court on 13 July 2018 (C-457/18). The government had consulted the Foreign Affairs Committee of the newly elected domestic Parliament on 9 July 2018. Acting Prime Minister Cerar publicly explained the official rationale of the lawsuit after the meeting:

The lawsuit is not an obstacle to the continued search for an implementation agreement that we want in Slovenia. [However, any] delay could send a completely wrong message, as if we either renounce legal remedies or we do not believe in our own arguments.

We will relieve politics of further tensions and thus transfer the matter to the legalprofessional level. Let the competent court decide on this matter, which means that at the political level we can develop relations with Croatia, and keep on looking for [a] solution for implementation. If we succeed [at the political level], then the [legal] action will be withdrawn. (STA News, 9 July 2018; emphasis added)

The original Slovenian complaint from 16 March 2018 of approximately one hundred pages (including supporting documents and media documentation) is confidential, so a detailed account of the legal and political reasoning appears impossible.

The lawsuit filed with the CJEU directly on 13 July 2018 contains the following elements, as summarised by the Court (Official Journal of the EU, C 399, 19-21, 5 November 2018; emphases added):

First plea in law:

By unilaterally falling short of the commitment, which it made during the EU accession process, to comply with the arbitration award and thus with the boundary delimited by that award and the other obligations imposed thereby, the Republic of Croatia refuses to respect the rule of law, which is a fundamental value of the European Union (Article 2 TEU).

By […] unilaterally refus[ing] to fulfil its obligations under the arbitration award, while at the same time preventing Slovenia from fully exercising its sovereignty over certain parts of its territory under the Treaty, the Republic of Croatia is in breach of its duty of sincere cooperation with the European Union and with the Republic of Slovenia as laid down in Article 4(3) TEU.

[…] The Republic of Croatia is making it impossible for the Republic of Slovenia to implement EU law throughout its mainland and marine territory and to act in accordance with that law, and in particular in compliance with the secondary Union rules relating to the territory of the Member States (first subparagraph of Article 4(3) TEU).

The Republic of Croatia is infringing Regulation (EU) No 1380/2013 of the European Parliament and of the Council of 11 December 2013 on the Common Fisheries Policy, and in particular the mutual access regime laid down in Article 5 thereof and Annex I thereto. The regime, which applies to Croatia and Slovenia since 30 December 2017, grants 25 fishing vessels from each country free access to the other country's territorial sea, as determined […] under the arbitration award. The Republic of Croatia is not permitting the Republic of Slovenia to exercise its rights under that regime and is thus infringing Article 5 of that regulation due to the fact that: (i) it is refusing to implement the mutual access regime; (ii) it is refusing to recognise the validity of the legislation adopted by the Republic of Slovenia for that purpose; and (iii) by systematically applying fines, it is denying Slovenian fishing vessels free access to the marine waters which the arbitration award of 2017 has defined as Slovene, and, a fortiori, free access to Croatian waters falling within the scope of the mutual access regime.

Fourth plea in law: 

The Republic of Croatia has infringed and continues to infringe Regulation (EU) 2016/399 of the European Parliament and of the Council of 9 March 2016 on a Union Code on the rules governing the movement of persons across borders (Schengen Borders Code). Croatia does not recognise the boundaries established by the arbitration award as a common boundary with Slovenia, is not cooperating with Slovenia to protect that 'external border', and is not in a position to guarantee adequate protection of that border, so that it is infringing Articles 13 and 17 of that regulation, and Article 4 thereof, which requires borders to be established in accordance with international law. Sixth plea in law:

The Republic of Croatia has infringed and continues to infringe Directive 2014/89/EU of the European Parliament and of the Council of 23 July 2014 establishing a framework for maritime spatial planning, which is to apply to 'marine waters' of Member States, as defined in accordance with the relevant provisions of the United Nations Convention on the Law of the Sea of 1982 ('Unclos') (Article 2(4) of the Directive). The Republic of Croatia rejects the arbitration award which has established that delimitation of the boundaries and -on the contrary -includes Slovenian waters in its own maritime spatial planning: consequently, it does not allow for harmonisation with the geographical maps of the Republic of Slovenia, thereby infringing that Directive, in particular Articles 8 and 11 thereof.

On 21 December 2018, Croatia filed a motion with the CJEU with regard to Slovenia's Article 259 lawsuit. The Ministry of Foreign and European Affairs communication focused on the aspect of the bilateral dispute being a matter of international law rather than EU law: […] Croatia is asking the ECJ to dismiss Slovenia's lawsuit as inadmissible, since the ECJ is not competent to decide on Slovenia's demands in proceedings envisaged under Article 259 of the Treaty on the Functioning of the European Union given that the dispute between Croatia and Slovenia should be settled by applying international law and that the settlement of the dispute does not depend on the application of the EU law or its interpretation. (Press release Ministry of Foreign and European Affairs of the Republic of Croatia, 21 December 2018) Croatia appeared to primarily uphold its position that the border issue is not settled under international law as Zagreb does not recognize the Final Award of the arbitral tribunal for the reasons outlined earlier (see e.g. Sect. 4.3.6.1). Following that logic, one could indeed take the view that the CJEU would not be competent since a (prospective) settlement of the border dispute as such under international law has prima facie nothing to do with the application of EU law. 128 In fact, Croatia's motion of inadmissibility was more comprehensive and based on three pillars altogether:

(i) The claims of Slovenia were only ancillary to the settlement of the bilateral dispute about the validity of the arbitration agreement and the arbitration award; (ii) the above dispute had to be settled according to the rules of international law which were not related to the application of EU law; 128 Nevertheless, even if the Final Award did not constitute a binding settlement under international law, there is a pertinent provision of EU legislation in so far as the mutual access to the territorial sea for fisheries purposes stipulated in Art. 5(2) of Annex I of Regulation 1380/2013 expressly refers to the decision of the arbitration procedure (the proceedings were ongoing by the time the Regulation was adopted). It would appear, therefore, that the above provision in Annex I constitutes a link to EU law rendering the settlement of the border mandatory for the application of the EU Regulation. This issue was broadly discussed at the CJEU hearing on inadmissibility on 8 July 2019 (author's field notes, 8-07-2019); see, however, Sect. 4.4.2 (ii)-(v).

(iii) the Court had no jurisdiction to rule on the validity or legal effects of either the arbitration agreement or the arbitration award both of which were not an integral part of EU law as the arbitration agreement was the real basis of the infringements of EU law pleaded by the Republic of Slovenia (Judgement C-457/18, 31 January 2020, paras 75-77).

The Court subsequently decided to separate the issues of admissibility and, should the necessity arise, the merits of the Case. A hearing on the issue of admissibility and jurisdiction was held before the Grand Chamber on 8 July 2019. The Advocate General presented its Opinion on 11 December 2019 recommending the Court had no jurisdiction. 129

The Court has examined whether it has jurisdiction, i.e. whether the arbitration agreement and the arbitration award are a matter of EU law and thus create obligations under EU competence. In its judgement of 31 January 2020, the Grand Chamber, inter alia, found:

(i) It was not competent to interpret an international agreement concluded by the Member States in an area outside EU competence, quoting from existing jurisprudence (C-132/09, Commission v Belgium), in particular when the pleaded failure to fulfil obligations is ancillary to the obligations from the very international agreement at issue (Judgement C-457/18, paras 91-92; 104); (ii) The Final Award handed down by the Arbitral Tribunal was governed by international law which was not within the EU competence, and that the EU was not a party to the subject matter despite its mediating role. Nevertheless, there was a clear link between the arbitration agreement and the arbitral proceedings on the one hand and the accession of Croatia to the EU on the other hand. However, those circumstances were insufficient to be seen as an integral part of EU law (Judgement C-457/18, para 102); (iii) The provisions in Annex II of the Act of Accession of Croatia to the EU referring to the Fisheries Regulation with regard to mutual access to the territorial waters of Croatia and Slovenia to be determined by the arbitration award did not mean that the commitments from the arbitration agreement were incorporated into EU law (Judgement C-457/18, para 103); (iv) It is within the competence of the Member States to determine the limits of its territories in accordance with international law, quoting C-111/05 (Aktiebolaget NN), that this principle was enshrined in Articles 52 TEU and 355 TFEU, and that the Member States have the competence for the geographical demarcation of their borders in accordance with international law (Judgement C-457/18, para 105);

(v) There was a clear obligation for the parties, i.e. the Republic of Croatia and the Republic of Slovenia, in Article 7(3) of the arbitration agreement, to take all necessary steps, including revising national legislation where necessary, to implement the arbitration award, within six months after its adoption, for the purposes of the mutual access regime provided for in the Fisheries Regulation 1380/2013, and that there was no doubt that implementation is pending (Judgement C-457/18, para 106); (vi) It is beyond the jurisdiction of the Court to examine the respective extent and the limits of the territories of the Republic of Croatia and the Republic of Slovenia by applying directly the border determined by the arbitration award (Judgement C-457/18, para 107); and (vii) Nevertheless, both the Republic of Croatia and the Republic of Slovenia have an obligation to "strive sincerely to bring about a definitive legal solution consistent with international law, as suggested in the Act of Accession [of the Republic of Croatia]" that ensures the application of EU law, and that an option to settle their dispute could be a submission "to the Court under a special agreement pursuant to Article 273 TFEU" (Judgement C-457/18, para 109).

The judgement on Slovenia v Croatia has some substantial precedent-setting characteristics since (i) it is the first Art. 259 TFEU Case Member State against a Member State on a territorial issue with a focus on the issue of jurisdiction of the CJEU, (ii) the territorial dispute was subject to third-party judicial dispute resolution under international law where the EU played a strong role in the drafting stages for the mandate for the arbitral tribunal, and (iii) the territorial dispute surfaced during EU accession negotiations. The following analysis of the judgement will tackle these issues in turn. It is clear from that case-law that the Court lacks jurisdiction to rule on an action for failure to fulfil obligations, whether it is brought under Article 258 TFEU or under Article 259 TFEU, where the infringement of provisions of EU law that is pleaded in support of the action is ancillary to the alleged failure to comply with obligations arising from such an agreement. (Judgement C-457/18, para 92; emphasis added) With reference to a previous judgement, the Court draws on the concept of ancillary, i.e. a legal argument used in an auxiliary or subordinate manner to seek the fulfilment of obligations stemming from a different area of law (international law, in this instance) than the one an Art. 258/259 TFEU claim is based on (EU law). The Court notes that, if infringement proceedings for failure to fulfil obligations relate to an international agreement which is outside EU competence, it has no jurisdiction on the interpretation of that agreement.

The concept of ancillary the Court subsequently employs with regard to the pleas of the Republic of Slovenia when stating that the infringements of EU law pleaded are ancillary to the alleged failure by the Republic of Croatia to comply with the obligations arising from a bilateral international agreement to which the European Union is not a party and whose subject matter falls outside the areas of EU competence. Since the subject matter of an action for failure to fulfil obligations brought under Article 259 TFEU can only be non-compliance with obligations arising from EU law, the Court, in accordance with what has been stated in paragraphs 91 and 92 of the present judgment, lacks jurisdiction to rule in the present action on an alleged failure to comply with the obligations arising from the arbitration agreement and the arbitration award, which are the source of the Republic of Slovenia's complaints regarding alleged infringements of EU law. (Judgement C-457/18, para 104)

The Court, by examining the relationship between the arbitration agreement and the arbitration award on the one hand, and the issue of the level of incorporation into EU law on the other hand, noted that it must be stated that the arbitration award was made by an international tribunal established under a bilateral arbitration agreement governed by international law, the subject matter of which does not fall within the areas of EU competence referred to in Articles 3 to 6 TFEU and to which the European Union is not a party. It is true that the European Union offered its good offices to both parties to the border dispute with a view to its resolution and that the Presidency of the Council signed the arbitration agreement on behalf of the European Union, as a witness. Furthermore, there are links between, on the one hand, the conclusion of the arbitration agreement, and the arbitration proceedings conducted on the basis of that agreement, and on the other, the process of negotiation and accession by the Republic of Croatia to the European Union. Such circumstances are not, however, sufficient for the arbitration agreement and the arbitration award to be considered an integral part of EU law. (Judgement C-457/18, para 102; emphases added)

The Court rightly acknowledges the (political and legal) link between the conclusion of the arbitration agreement and the accession of Croatia to the EU and also the role of the EU in the settlement of the border dispute. Nevertheless, the Grand Chamber falls short of recognising the true performance of the EU institutions in that process. Regrettably, "good offices" inadequately and insufficiently describes the undertakings of the European Commission and the Council Presidency. In established third-party conflict resolution, good offices equals allowing for the parties to communicate directly with one another but with almost zero intrusion by the third party, with little active control over the process and the substantive issues, and without the third party making any proposals (see e.g. Sects. 1.3.1.1 and 1.3.1.4) .

As a matter of fact, however, the European Commission did play an active role as a mediator/facilitator in the travaux préparatoires of the Arbitration Agreement. This was not least expressly acknowledged in the Agreement's Preamble ("Welcoming the facilitation offered by the European Commission"). Precisely, as this author has demonstrated, the Commission prepared two drafts of the Arbitration Agreement (Rehn I and Rehn II)-following an initial draft for a mandate for a Senior Experts Group-and discussed them with the parties in various meetings and through written correspondence including amendments to the drafts by the parties. That phase, where the European Commission brokered the lion's share of the later Agreement, lasted from January to June 2009 (see ).

In addition, from July to November 2009, the Swedish EU Presidency assisted the parties in their bilateral finalising of the Arbitration Agreement. The Swedish Presidency's positive facilitating role, which included the country's Foreign Minister and State Secretary, has been expressly acknowledged to this author by both parties. During the Swedish Presidency, a remaining obstacle ahead of concluding the Agreement was removed: the issue of the potentially prejudging Croatian documents from the accession negotiations with reference to the common State border. An exchange of letters between the Croatian Prime Minister and the Swedish Prime Minister in his role as EU Council President defused the issue. The drafting of that letter had taken several weeks and involved members of the bilateral Croatian-Slovenian Silent Diplomacy Group, the Swedish State Secretary and the Swedish Prime Minister (see Sect. 4.2.5) . The role of the Swedish Presidency was officially recognised by signing the Arbitration Agreement as a witness together with the parties on 4 November 2009, as the Court correctly finds. With regard to the obligations under international law arising from the arbitration agreement and the arbitration award in the context of EU legislation, the Court further observes that [i] n the case in point, Article 7(3) of the arbitration agreement provides that the parties are to take all necessary steps to implement the arbitration award, including by revising national legislation, as necessary, within six months after the adoption of that award. Furthermore, the footnotes relating to points 8 and 10 of Annex I to Regulation No 1380/2013 state that, as regards the Republic of Croatia and the Republic of Slovenia, the regime, laid down in that annex, governing access to the coastal waters of those Member States under neighbourhood relations 'shall apply from the full implementation of the arbitration award'. It is not in dispute, as the Advocate General has also observed in essence in point 164 of his Opinion, that effect has not been given to the arbitration award. (Judgement C-457/18, para 106; emphasis added) Whilst the Court expressly states the implementation obligations of the parties arising from the arbitration agreement, it also observes that the application of the fisheries regime for the territorial waters of Slovenia and Croatia respectively is subject to the full implementation of the arbitration award. What the Court appears to have avoided, however, is to interpret the Act of Accession of the Republic of Croatia. Such interpretation would have had to include a broader taking into account of the arbitration award as part of the link between Croatia's accession to the EU and the resolution of the border dispute. A true interpretation of the Act of Accession could have gone beyond a mechanistic reading of the footnotes in the Act of Accession and the Fisheries regulation.

In relation to the competence for territorial issues, including the delimitation and demarcation of borders, the Court notes that it is for each Member State to determine the extent and limits of its own territory, in accordance with the rules of public international law (see, to that effect, judgment of 29 March 2007, Aktiebolaget NN, C-111/05 […], paragraph 54). Indeed, it is by reference to national territories that the territorial scope of the Treaties is established, for the purposes of Article 52 TEU and Article 355 TFEU. Moreover, Article 77(4) TFEU points out that the Member States have competence concerning the geographical demarcation of their borders, in accordance with international law. (Judgement C-457/18, para 105) As a result, it appears that the fact that (i) the arbitration award has not yet been implemented, (ii) there nevertheless is an implementation obligation from international law, however not from EU law, and (iii) the Member State competence for territorial issues, has led the Court to the finding that [i] n those circumstances, it is not for the Court -if it is not to step beyond the powers conferred upon it by the Treaties and encroach upon the powers reserved for the Member States regarding geographical determination of their borders -to examine, in the present action brought under Article 259 TFEU, the question of the extent and limits of the respective territories of the Republic of Croatia and the Republic of Slovenia, by applying directly the border determined by the arbitration award in order to verify the existence of the infringements of EU law at issue. para 107) and that therefore it must be held that the Court lacks jurisdiction to rule on the present action for failure to fulfil obligations. (Judgement C-457/18, para 108) It must be noted, that, in conclusion, the Court nevertheless explicitly states that Art. 4(3) TEU, enshrining the principle of "sincere cooperation", creates an obligation to bring about a definite settlement of the dispute in practice:

This conclusion is without prejudice to any obligation arising -for both of the Member States concerned, in their reciprocal relations but also vis-à-vis the European Union and the other Member States -from Article 4(3) TEU to strive sincerely to bring about a definitive legal solution consistent with international law, as suggested in the Act of Accession, that ensures the effective and unhindered application of EU law in the areas concerned, and to bring their dispute to an end by using one or other means of settling it, including, as the case may be, by submitting it to the Court under a special agreement pursuant to Article 273 TFEU. (Judgement C-457/18, para 109)

The above concluding paragraph, however, leaves the observer somewhat puzzled. First, the Court refers to the Art. 4(3) TEU principle of sincere cooperation implying a real effort from both parties to bring about a definitive legal solution, as stipulated in Croatia's Act of Accession to ensure the territorial application of EU law. This appears to be a clear reference to the fact that implementation of the arbitration award is indeed pending. Second, the Court calls on the parties "to bring their dispute to an end". Here, the Court appears to refer not to the initial dispute over the common State border which is res judicata, but to the fact that one party, the Republic of Slovenia, insists on the implementation of the arbitration award, a binding settlement under international law, whereas the other party, the Republic of Croatia, does not recognise the arbitration award.

Third, as for the settlement of that dispute, the Court suggests "using one or other means of settling it", including a joint submission to the Court under Art. 273 TFEU. However, it is difficult to see the motivation of either party to settle their difference of opinion about the obligations arising from the Final Award. Slovenia can rely on the well-established fact that the award is a binding settlement under international law (see Art. 7(3) arbitration agreement which the Court quoted in para 106; see also e.g. Bantekas 2015: 109-112; Tanaka 2018b: 106; 109; Degan 2019). Croatia, for its part, may be expected to want to avoid its position of non-recognition of the award being repudiated by a judicial body. Nevertheless and in theory, the two parties could bring the matter before the ICJ (under Article 36(1) of the Model Rules on Arbitral Procedure) or indeed before the CJEU under Art. 273 TFEU. In practice, however, it would appear unlikely for obvious reasons that the two parties could reach agreement on a joint submission under the present circumstances.

Not unexpectedly, the decision of the EU Court of Justice was received differently in Croatia and in Slovenia.

The Slovenian Foreign Minister, Miro Cerar, said:

This is a clear message that the course of the border between the two countries has been determined […] . Today, the Court explicitly confirmed what Slovenia has claimed all along and what no country has denied: the Arbitral Award is applicable and binding, both countries must implement it. This is yet another proof -and that from the top legal institution of the EU -that Slovenia was right in arguing that Croatia, too, must implement the Arbitral Award.

(Slovenian Ministry of Foreign Affairs news 31 January 2020)

The Croatian Prime Minister, Andrej Plenković, said:

Croatia [is] neither called upon in this ruling to implement the arbitration agreement, nor can Slovenia resolve this matter on its own. That's the key, the gist of today's message. Croatia is taking this opportunity to reiterate its invitation to Slovenia to resume bilateral talks in search of a final solution to the border issue which objectively is not far away, but which is challenging because both parties need the support of their respective parliaments to ratify an agreement. (HINA news 31 January 2020)

The impact of the Court's judgement on the immediate obligation to start implementing the arbitration award is obviously being interpreted in a different manner by both sides. Nevertheless, there appears to be some kind of common understanding that the issue is now at the bilateral level and that there is no solution but in the bilateral sphere.

For the time being, however, any bilateral follow-up to the CJEU judgement seems absent due to the overriding preoccupation with the coronavirus crisis management. Still, the decisive question for a final bilateral agreement indeed is the threshold of parliamentary ratification, in particular the two-third requirement in the Croatian Sabor, a fact that the Slovenian side is well aware of (interview senior Slovenian civil servant, 17-04-2020).

In the words of the current Foreign Minister of Slovenia:

[…] The ruling of the Court of Justice of the EU should be seen as a call on Slovenia and Croatia to resolve the issue in accordance with international law, as stipulated in the Act of Accession of Croatia to the EU […]. Slovenia will continue to seek dialogue with Croatia in view to resolve the open issues and enhance bilateral cooperation. There is, of course, no timeline; it would only raise false expectations. (Letter Anže Logar to the author, 17 April 2020)

The concluding analysis of this core Chapter will sum-up developments within each of the four phases. Corresponding to the research questions that this study is based on, the analysis of the developments employs the process-tracing toolbox of conflict issues, conflict dynamics, conflict management, actors in the conflict, and EU power issues (see Sect. 1.3). For a comprehensive feedback as to the individual theory strands of the analytical framework see Chap. 5.

The early phase: post-independence bilateral stock-tacking

The conflict issues: As to the origins of the conflict, the (conflictual) dismemberment of Yugoslavia created a new conflict. Fundamentally, the independence of both countries in 1991, i.e. the visible beginning of the territorial end of the Socialist Federal Republic of Yugoslavia (SFRY), is the new conflict's starting point. Internal SFRY republican borders were going to become international borders. All of a sudden, what used to be administrative or cadastral borders became distinct territorial and, thus, also political borders. Perhaps largely unnoticed, the location of the new Slovenian border-crossing at Sečovlje-Plovanija was the first territorial point of contention between the two countries as early as June 1991, on the eve of the declarations of independence. This is an example of the situation on land. At sea, no formal partition by Republics whatsoever existed in the Yugoslav maritime space. Still, it was only in the spring of 1993 when sovereignty over Piran Bay and access to the high seas became a salient issue in the Slovenian parliament. The response of the Croatian parliament followed six months later, a matter for which allowance must be made for the fact that the country was busy with the fully-blown Homeland War over territory in large parts of its hinterland where Croatian State-building was yet to be completed. Nevertheless, the issues at stake in the border conflict with Slovenia were now plain to see. By the autumn of 1993, the dispute over Piran Bay and the maritime border as regards access to the high seas for Slovenia was fully established. Furthermore, the interests of the parties had been put on the table, too, and there was no doubt about the competing sovereignty claims of either side. With regard to conflict dynamics, one can clearly talk of a stable initial phase where positions evolved, and a low level of intensity as positions were exchanged below the political level. The conflict management mode was purely bilateral, and the main setting was the technical level. A rich body of bilateral expert groups, the actors in the conflict, was up and running by then and going through a screening phase. The expert groups were able to identify the strips and spots along the border where the cadastral limits were not aligned. As a result, there was a solid account of the disputed sections of the common State border outlined in the Expert Group Report from December 1996. One may therefore posit a pragmatic stance taken by both sides towards the border issue in the early phase. After all, cross-border life is what matters to citizens on the ground where relations had been very close for many decades during Yugoslav times and thereafter. However, the maritime border was not yet part of the bilateral talks. Still, any progress in terms of clearing up the substantive dispute over the land border proved difficult. This is why the expert group talks stalled in mid-1998. Croatia and Slovenia subsequently launched an attempt at third-party mediation by a former senior US politician in the early summer of 1999. That move proved fruitless, however.

A fresh start on the bilateral level was made in early 2001. In fact, it was an effort to find a comprehensive bilateral settlement at the highest political level. In terms of actors in the conflict, therefore, it was a clear shift from the technical to the political level accompanied by a novel behavioural conduct of good-neighbourly spirit and a sense of de-escalation on both sides. Likewise, there was a new momentum of conflict dynamics, as fully fledged negotiations between the heads of government must be seen as a very real opportunity to resolve the dispute. Indeed, in a remarkable move, by-passing traditional diplomatic channels of communication, the two prime ministers Drnovšek and Račan were sitting together determined to arrive at a fully negotiated settlement. It must be noted that political will and a special level of mutual respect and trust were indispensable prerequisites for that to happen. It remains a "chicken and egg" question, however, whether Račan should have taken the opposition and the law-of-the-sea establishment on board much earlier to secure domestic support in Croatia for a bilateral deal, or whether the secrecy of the talks was the only way to arrive at an agreement at all in the first place. As for conflict issues, the maritime border, however, became even more contentious in the end. One may argue that the sea-border solution foreseen in the Draft Agreement was perhaps too far away from what the political elite in Croatia considered or perceived as legitimate at the time (and certainly would today), a notion of great sensitivity only three years after the full re-integration of the territories in Slavonia and the Krajina. In any case, the fact that both a novel and contentious solution of the maritime border failed, hardened the positions, and rendered the conflict an intractable one, also leading to a new dead-lock in terms of conflict dynamics.

Too good to be true: the failed effort to submit the dispute to the ICJ Over the following years there were no efforts whatsoever at finding a resolution. Thus, the conflict dynamics were in cooling-off mode. Only in 2007, the actors in the conflict being the heads of government (i.e. the highest political level), was the new (bilateral) effort to submit the dispute to the International Court of Justice (ICJ) made. Somewhat ironically perhaps, after the ex-post burial of the Drnovšek-Račan Draft Agreement in Croatia, one could witness a similar turn of events in Slovenia after the Bled Agreement. The 2007 accord between Janša and Sanader at first appeared to be a pragmatic and workable agreement. After all, it would have been very difficult to go down the path of bilateral negotiations again, where there was hardly any room for face-saving manoeuvres bearing in mind the failure of the 2001 Draft Agreement. So, for a moment at least, the new conflict management mode was a bilaterally and voluntarily agreed submission to third-party resolution. However, the new conflict issue now was the terms of submission to third-party resolution. It turned out, during the technical-level drafting stage of the mandate for the Court, that a submission to the ICJ which-in its deliberations on the merits-would be restricted to international law rather than equitable principles, was apparently an untenable approach for the Slovenian government. This was because it seems Slovenia considered it necessary to have room for equity in order to achieve access to the high seas. At the end of the day, the task of agreeing on a mandate for a court does require bilateral agreement and that is where the process yet again stalled. As a result, the conflict dynamics mode yet again levelled up. It remains obscure, however, to what degree the focus of attention of the Slovenian side may have already shifted to the 'golden opportunity' of using the leverage of veto power (that decision being taken in June 2008) in Croatia's EU accession negotiations, which were going on in parallel, a vital EU power issue indeed.

Now or never: forced delegation of conflict management in a hybrid line-up It was in the autumn of 2008 that Slovenia transferred the bilateral border dispute onto the EU stage through Ljubljana's veto during Croatia's accession negotiations. With regard to conflict actors, the technical level (the Council Working Group on Enlargement COELA) was in the driving seat. As for the new conflict issue, the prejudging maps in the Croatian accession negotiations documents were the official reason. The real interest of Slovenia, however, was to solve the border dispute ahead of Croatian EU accession. It appears fair to say that this is the first instance in the history of the border dispute that the official claims and the real interests of a party to the dispute diverge. In terms of EU power issues, also the first time that they appear, inserting a bilateral issue into EU accession negotiations amounted to nothing less than linking the border dispute to the EU acquis despite the fact that it had nothing to do with the acquis. As a result, a bilateral (territorial) issue with a Member State became an add-on to the (political) conditionality of EU accession for the first time ever. Such was the new conflict issue likewise. With regard to conflict management, the third-party role entered the scene. Within the remit of the intergovernmental level, the French EU Council Presidency was facing, at first hand, the unique circumstances of a Member State using its status as a Member State vis-à-vis a Candidate Country, i.e. blunt blackmailing, and this proved to be an unsurmountable task at the technical level. From a conflict-dynamics point of view, the level of escalation may be seen on a new all-time high as it was no longer a bilateral conflict, but also one that had directly affected the EU level.

The following phase marks a completely new line-up in terms of conflict management. The EU's Enlargement Commissioner Olli Rehn took over by the beginning of 2009, stepping into what was terra incognita in the history of EU accession negotiations: clearing the accession process of a bilateral issue by means of third-party dispute resolution. To be sure, it was a hybrid set-up of third-party mediation and bilateral negotiating. The Commission itself took on the role of mediating third party in the first place. After an unsuccessful attempt at soft mediation, Rehn and his legal team managed to produce drafts of the later Arbitration Agreement seeking to take on board the vital interests of both Slovenia and Croatia. The conflict issue, very much like in the post-Bled phase around 2008, was the terms of the mandate for the third-party judicial body. The first of two crucial issues, the task of the arbitral tribunal, i.e. to secure access for Slovenia to the high seas whilst preserving classical approaches of international law for the maritime border and for the land border, the Commission managed to hammer out with great expertise in the first half of 2009. To that end and in terms of actors in the conflict, one can say with some accuracy that it was the European Commission who was running the management of the conflict and that it was running it at its own initiative. As for conflict dynamics, one may posit that the conflict was on a stable level whilst it was, by and large, being treated constructively also by Croatia and Slovenia over the first half of 2009.

After a brief stalling of the process at the beginning of July 2009, the finalising phase, with regard to conflict management, saw a re-bilateralisation of the negotiations skilfully facilitated by the Swedish EU Council Presidency. The second crucial development, widely perceived as a game-changer in terms of a great face-saving and de-escalating opportunity of conflict dynamics, was the new sequencing of (i) Croatian accession and (ii) the start of the arbitration procedure. It appears fair to say that it was the reversal of the original order, i.e. the lifting of the Slovenian veto and the idea to have the Croatian Accession Treaty signed first before starting the actual arbitration procedure, which rendered the finalisation of the Arbitration Agreement possible. In other words, the new sequence solved the conflict issue (delaying Croatian EU accession until the end of a future arbitration procedure) of the second drafting stage of the Arbitration Agreement. It is important to note that this was predominantly achieved in a bilateral manner, so the conflict actors were the two parties to the conflict. Indispensable prerequisites were the high level of mutual trust both between Kosor and Pahor and between the prime ministers' negotiator-advisors. Nevertheless, one must recall that the unilateral declaration upon Croatian ratification of the Arbitration Agreement was a sign of the asymmetry in the power relationship between Croatia as a Candidate Country and Slovenia as a Member State at the time, in particular in the context of the great unease with and enormous conflictual potential of territorial issues in Croatia. EU power issues, on their part, were successfully dampened, and it seemed that the conflict was finally going to be contained by the conclusion of the Arbitration Agreement.

To hell and back: the arbitration procedure heavily bruised but alive With regard to conflict dynamics, it is easily forgotten that the arbitration procedure had a smooth start indeed. The arbitral tribunal was formed in a constructive and timely manner on the bilateral political level at the beginning of 2012. The subsequent written submissions for the judicial procedure were comprehensive, also containing replies to the counter-memorials. Equally, an extensive two-week hearing provided the parties with ample opportunity to raise any point that they wished to raise. In terms of conflict issues and the result, not only the Tribunal but also the parties themselves were fully in the picture of all arguments and real interests of the parties presented for the Tribunal's deliberations on the merits. One can say with some accuracy, too, that the conflict management was firmly in the hands of the Arbitral Tribunal as the third-party judicial body with the parties submitting their claims in written form and during an extensive hearing.

The summer of disruption saw the arbitration procedure implode at the end of July 2015, which left the actual proceedings heavily tainted politically and moved the conflict dynamics to yet another peak. As collateral damage, the events affected the reputation of international arbitration as such, still a major and successful dispute settlement tool, at least temporarily. It may be morally questionable and perhaps unethical, and certainly unlawful vis-à-vis domestic Slovenian law, to tap into the communication of government actors, all the more so from a State that one is supposed to enjoy good-neighbourly relations with. Then again, it simply goes against the express confidentiality provisions of the arbitration procedure, and is therefore unlawful, to engage in ex parte communication (the new conflict issue) with a Tribunal member in the first place. This piece of illegal communication resulted in unprecedented outrage among the political elite in Croatia, leading to the unanimously adopted Sabor resolution asking the government to leave the arbitration procedure, which it did. As regards actors in the conflict, the entire political level in Croatia was one dominating player (the government being in the driving seat, of course) in late July 2015, another one being the arbitrator appointed by Slovenia and the Slovenian Agent and their revealed pieces of communication from November 2014 and January 2015 (ex ante, as it were). The third actor was the Arbitral Tribunal which had to assess the implications of the Croatian de facto withdrawal from the arbitral proceedings.

The legal arguments of the Croatian side, however, were not very strong. The weakest of them was to challenge the jurisdiction of the Arbitral Tribunal to look into the termination request. It is a well-established fact that international courts and tribunals do possess the compétence de la compétence to decide themselves not only about the merits of a case, but also on procedural matters. The fact that Croatia no longer participated in the arbitral proceedings followed the political logic-and indeed the express request-of the Sabor vote, but not the legal reality. In addition, the reconstituted Tribunal, which no longer had party-appointed arbitrators but five neutral members, had increased the Tribunal's independence and legitimacy. In terms of conflict issues, the new point of contention now was the gravity of Slovenia's violation of the Arbitration Agreement. Croatia (notwithstanding its legal argumentaire) considered the violation as fundamental and absolute thus legitimising Zagreb's move to terminate the Arbitration Agreement and the arbitral proceedings, whereas the Tribunal, in its Partial Award in June 2016, had to assess and did assess the impact of Slovenia's ex parte communication from a strictly legal-procedural point of view for which it had jurisdiction. From a conflict-dynamics point of view, the stance had hardened further by the time the Final Award was handed down in June 2017. Croatia had boxed itself into a corner where no face-saving move was possible despite the fact that the substantive contents of the Award was not unfavourable to Croatia. The military installation at Sveta Gera was going to "come home", the status of the Dragonja strip on the left bank of the river was confirmed to be Croatian, and the maritime border departure from the equidistance line in favour of Slovenia must be seen as modest. The partition inside Piran Bay appears to properly reflect its use in 1991, and even the corridor regime inside the Croatian territorial waters for the purposes of providing unhindered communication between the high seas and the Slovenian territorial sea can be regarded as very close to the Croatian position set out in the written submission of the arbitration proceedings. Nevertheless, the sobering news was that, after the arbitration procedure that was supposed to settle the matter, the border conflict was more intractable than ever before.

It is difficult to say whether any of the parties seriously believed that efforts to achieve bilateral implementation of the Final Award would bear fruit. In terms of conflict issues, the largely contradicting real interests of the parties were as follows: the Slovenian government had an internationally binding Final Award at hand, which in its substantive points was not much more than the access to the high seas which had been de facto secured by the Arbitration Agreement in the first place. The Croatian government, for its part, needed to avoid at all costs any one-to-one implementation of the (not so unfavourable) Award for the principle reason that it could not recognise the arbitral award as such due to the unanimous 2015 Sabor vote. In the period between July 2017 and March 2018, the actors-in-the-conflict line-up was bilateral, again searching for implementation of different kinds. The parties were in touch, although the road was rather rocky. Nevertheless, it is fair to say that the conflict dynamics were somewhat dampened during that period.

Fundamentally and further to the real interests of the parties, the consideration of the political costs of direct implementation apparently carried more weight in Zagreb than the benefits of a once-and-for-all settlement of the border with the EU neighbour Slovenia. This decision must be seen against the background of Croatia's application to join the Schengen area and the Eurozone for both of which Slovenia's support is needed due to the unanimity requirement in Council for those areas. In a similar vein, the political costs for any Slovenian government to sustain bilateral talks with Croatia on implementation that were likely to lead nowhere seem to have been calculated as too high. It does not take a deterministic view, therefore, to suggest that there was no alternative for Slovenia other than going to the European Court of Justice to seek implementation of the arbitration award-which it did not receive.

Competent or not? The issue of jurisdiction sends the conflict back to square one Slovenia's decision to go to the EU Court of Justice rendered the matter a fully fledged EU power issue. In fact, the Slovenia-Croatia border dispute had now become a question of application of EU law, an issue perhaps unthinkable when it first appeared on the EU stage in autumn 2008. With regard to conflict management, the CJEU as a third-party judicial body became involved at the request of one of the parties. It is crucial to note, however, that the European Court of Justice is not an international court of appeal, i.e. it could not look into the substantive decision of the Arbitral Tribunal (which is a definite settlement of the case under international law), but was invited to assess the Slovenian claims of failure to fulfil obligations of EU law on the part of Croatia. To that end, the conflict issue here (between Croatia and Slovenia) in very fundamental terms was whether the implementation of the Final Award is mandatory to fulfil the obligations of applying EU law.

The Court, as the competent body to interpret EU law, decided to investigate the issue of admissibility first. To that end, the conflict issue was narrowed down to the question of how strong the link between the arbitration procedure and the reference to its implementation in the EU Fisheries Regulation was. This issue was extensively discussed during the hearing at the Court in July 2019. With regard to conflict dynamics, the "battle-field", as it were, was now one of jurisdiction. The level of conflict was high again, albeit confined to the argumentation before the Court. In addition, one can contend that the conflict had escalated by the decision of the Court, now the sole actor in the conflict, to address the issue of admissibility first. With regard to the management of the conflict, this decision presented two clear-cut alternatives. The Court would either manage the conflict-if it decided in favour of admissibility, or it would not-if it decided it had no jurisdiction. At the same time, this juncture virtually killed off any face-saving options. The parties and the wider public alike were confronted with a clear win-lose scenario: If the Court declared the Slovenian claim admissible, Slovenia would be the clear winner with well-founded expectations that the Court would largely endorse the country's claims on the merits later on. If the Court decided that it had no jurisdiction, Croatia would be the clear winner.

With the judgement of the Court handed down, the conflict is clearly back at the bilateral level. The actors in the conflict are now the governments of Croatia and Slovenia. They are in charge of the management of the dispute again. In view of the fact that the conflict about the validity of the arbitration award remains, it appears that, for the foreseeable future, it is impossible to make any prediction, neither in terms of the conflict dynamics nor as for the possibility of an agreement at all.

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State Secretary in the Ministry of Foreign Affairs of Sweden 2005-2014. Phone interview

Chair of the Foreign Affairs Committee

Professor for International Law, Naples University. President of the International Association of the Law of the Sea. Phone interview

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Civil servant involved in the trilateral meetings during the French EU Council Presidency in 2008. Phone interview

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European Commission civil servant

European Commission civil servant in charge of the accession negotiations with Croatia

European Commission civil servant involved in the Enlargement Strategy

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