key: cord-0720167-bd6ba0cp
authors: Johnstone, Phil; McLeish, Caitriona
title: World wars and the age of oil: Exploring directionality in deep energy transitions
date: 2020-09-04
journal: Energy Res Soc Sci
DOI: 10.1016/j.erss.2020.101732
sha: 7ba6f182b034ff2d760e7361f26b3c8f5b10ed11
doc_id: 720167
cord_uid: bd6ba0cp

This paper explores the role of the world wars in 20th century energy transitions, focusing on the growth of oil as a major energy source which accelerated after the Second World War in North America and Europe. We utilise the recently developed Deep Transitions framework which combines Techno-Economic Paradigms and sociotechnical transitions approaches. The first deep transition entails the long running emergence of industrial modernity since the late 18th century which culminated in the post-Second World War economic ‘golden age’ underpinned by rapid and stable growth and prosperity in North America and Western Europe. The Deep Transitions framework draws attention to the increasing role of fossil fuels over this long period, and how fossil fuel consumption accelerated in the 20th century taking on a particular direction where energy, mobility, and food systems became increasingly reliant on oil while the share of coal as a proportion of the energy mix decreased. This paper integrates sociotechnical, historical and geopolitical literatures to examine how the development of the age of oil was shaped by wartime demand pressures and logistical challenges and the search for new solutions to these challenges in the United States of America and the United Kingdom.

The post-World War II era saw the share of oil in energy consumption rapidly increase with abundant supplies of oil products seen as key in underpinning the so-called 'golden age' of economic development [1] . The 'golden age' constitutes a sustained period of stable economic growth, increased prosperity, and the rise of mass consumption in North America and Europe, lasting until the oil crisis of 1973. While energy transitions occurring during this post-World War II era have often been a point of focus, until recently, as Evenden [2] points out, there has traditionally been a smaller proportion of studies focused on how wartime activities have influenced energy system change. In recent years however, there is a growing sub-set of literature that has focused on the importance of world war as a factor in energy transitions [2] [3] [4] [5] . Elsewhere, in the fields of history and geopolitics, there has been significant attention on oil resource geographies, developments in oil technologies, its uses, industry, infrastructures, logistics, and patterns of import and export during wartime [6] [7] [8] [9] [10] . This paper contributes to emerging literatures on war and energy transitions [3, 4, [11] [12] [13] , integrating insights from historical and geopolitical literatures with sociotechnical perspectives to understand the role of world war in the 20th century development of the 'age of oil' [14] .

In doing so, this paper builds on the 'Deep Transitions framework' (here on in "DT") introduced by Schot and Kanger [15] . The DT framework is relatively new and constituted by several key concepts which we discuss in more detail in Section 2.2, however we will now briefly outline some key features. The DT framework combines the Techno Economic Paradigms (TEP) approach developed by Carlota Perez [14] , and sociotechnical transitions theories utilising the Multi-Level Perspective (MLP) [16] . Both the TEP approach [17, 18] and the MLP [19, 20] have been frequently drawn upon to understand energy transitions.

The TEP approach builds on long wave theory which has been widely used in economics for several decades [21] , and identifies different phases of economic development referred to as 'great surges' of development. These are depicted as generally occurring over 40-60- year periods, and are driven by the unleashing of particular technological innovations (such as the internal combustion engine); a paradigm of economic growth that coordinates activity (such as 'mass production'); particular patterns of financial investment; and a source of cheap energy which underpins each surge of economic growth. For the purposes of this study, the most relevant point to note is that TEP framework specifically names the period from 1908 to 1971 as "the age of oil, the automobile, and mass production", where "the cheapening of oil-based fuels, electricity and road transport gave positive support to the very high growth rates of national mass markets" ( [14] : 136). The TEP framework has generally focused at the 'macro' level of analysis entailing broad changes in entire economies driven by technological innovation and cycles of financial investment.

Analysis drawing on the MLP on the other hand, has focused at the level of 'sociotechnical systems' oriented around the provision of societal needs such as energy or mobility. Different elements including technology & science, markets & users, industry, institutions & regulations, shape activities within a sociotechnical system [15] . MLP approaches tend to focus on how novel technologies and practices operating in protective environments called 'niches' can, overtime, come to destabilise 'sociotechnical regimes', which represent the dominant technological and institutional configurations through which a particular societal need is delivered. Rather than the 'macro' approach of TEP, the MLP's focus on individual sociotechnical systems is understood as a 'meso' level approach. The framework has been used to examine the co-evolutionary dynamics of important historical technological changes including the transition from sailing ships to steam ships [16] , as well as historical analysis focused on the long-term decline of previously dominant technologies such as the case of the UK coal industry in the 20th century [22] .

However, while world wars are mentioned as relevant exogenous factors in both TEP and MLP literatures, activities during world war and the sociotechnical implications of wartime have generally not been a focal point of analysis. The DT framework addresses this gap, with one of its key propositions (proposition 7) being that 'external shocks' and particularly world wars, are decisive 'turning points' in coordinating multiple sociotechnical systems (energy, food, and mobility) in a similar direction.

The notion of 'directionality' is central to the DT framework. Building on the work of Stirling [23] , Schot & Kanger outline their understanding of the term as follows: "socio-technical change has a direction, choices are made between directions and actors gradually become blind to alternatives, which is a central tenet of much of the innovation studies literature" ( [14] : 1045). Thus, a focus on 'directionality' recognises the plurality and diversity of potential energy transitions and is attentive to historically contingent factors whereby certain energy trajectories become dominant and alternatives are 'closed down'. The closing-down of alternative pathways occurs as technological market structures, regulations, political support, infrastructure, and user practices, align to form a particular technological trajectory that gains momentum and makes it challenging for new technologies and practices to break through [23] .

To take one example, electricity grids designed around constant 'baseload' production utilising increasingly large power plants often located far from where there is most demand, made it very challenging for variable renewables and energy conservation measures to break through in many countries without concerted political pressure over several decades [24] . Accordingly, energy transitions usually take several decades and are fraught with political struggles, resistance by existing energy incumbents, and usually require governmental intervention to overcome these barriers [25] .

However, a key distinction with regards to the understanding of directionality in the DT framework is the focus on the co-evolution and alignment of multiple sociotechnical systems, as compared to the tendency in sociotechnical approaches to focus on single systems [26] . The notion of directionality is further refined in the DT framework through the concept of rules, which is a well-established concept used in institutional studies and a core concept of the MLP. Schot and Kanger define rules as "humanly devised constraints that structure human action, leading to regular patterns of practice" ( [14] : 1053). An example of a rule given by Schot and Kanger is an "imperative to use fossil fuels". After the Second World War this rule became dominant in energy, food, and mobility and therefore constitutes a 'meta-rule' because the rule structures human action and influences regular patterns of practice in multiple sociotechnical systems rather than a single system.

Another meta-rule relevant to this study identified elsewhere [27] is the "imperative to maintain abundance and constancy of supply", which became particularly pronounced during the intense demand pressures of the First and Second World Wars, where the ability to maintain supplies of key materials to the front lines meant the difference between victory and defeat. Historians have pointed out that after the Second World War an era of "energy abundance" based on cheap oil emerged in the USA [28] [29] [30] , and then in many European countries as "the years of surplus" from 1955 onwards [31] . The expansion of oil and a system of energy abundance are closely linked [28] .

In this paper we combine geopolitical and historical literatures with sociotechnical approaches to understand how the heightened conditions of maintaining abundant and constant supply during the First and Second World Wars influenced the emergence of the 'age of oil' identified as being a key element in the fourth surge by Perez which forms the culmination of the first deep transition. The overall research question is as follows: what was the role of world wars in shaping the emergence of the age of oil in the culmination of the first deep transition?

Building on diverse literatures from geopolitics and history, it is possible to build a plausible and evidence-based narrative to address this question. In undertaking this analysis, there are two central aims. The first is to contribute to the emerging literature on energy transitions and the role of world war. The second aim is to respond to proposition 7 of the DT framework, concerning the key role of war in the coordination and alignment of sociotechnical systems.

We proceed as follows: Section 2 situates this paper in the wider context of the broad field of 'energy transitions' research, and specifically the emerging interest in wars and the military as key factors in energy transitions. We then discuss the DT perspective in more detail, explaining key concepts and how discussions of deep transitions align with and can contribute to energy transitions literatures. In Section 3, after discussing our approach, we outline an interpretive analysis drawing on extant literatures from history and geopolitics to build an interpretive evidence-based account of the role of the world wars in the emergence of the age of oil, focusing on World War I, the inter-war years, World War II, and the post-war period of re-orientation and reconstruction.

This study focuses on the United States (USA) and the United Kingdom (UK). This focus is motivated by two observations. First is the fact that core to Perez's theorisation of the age of "oil and mass production" is the lead role played by the USA and how oil-dependent forms of economic activity 'diffused' to Europe. Second, is that historic accounts of oil developments and geopolitical struggle highlight the central role played by relations between the USA and the UK -both as a point of friction and collaboration [7, 32] -in 20th century oil developments. This focus is not to diminish the importance of oil developments in other countries, and -perhaps unsurprisingly given the nature of war and geopolitics -we do refer to the strategies of other belligerents in the analysis below. However, the main focus on USA-UK oil developments provides a necessary boundary (given the breadth of this topic) to focus more specifically on sociotechnical responses during war, and also explore international dynamics of friction and collaboration between the two countries identified as a significant factor in historical studies [7, 10, [32] [33] [34] . However, as we discuss, the changing relations between these two countries over the course of the fourth surge and after the Second World War also has important implications for understanding rapid oil transitions in Western Europe in the context of Post-World War II reconstruction.

We are aware of the geographical limitations of the present study. Our focus is on breadth rather than depth (covering a time period entailing two world wars), and so there will necessarily be gaps in the analysis. Entire sub-fields of historical analysis are devoted to just one war, or even a war in a particular country. However, we seek to contribute to opening up for further elaboration and testing, propositions that can contribute to emerging discussions around energy transitions and world war, through answering the question of the role of world war in influencing the directionality of the first deep transition. While history is not a guide to the future, we argue that the historical imagination [35] can contribute to enriched discussions in energy transitions on possible drivers and mobilising forces for sustainable energy transitions.

We now situate the present study in the wider field of energy transitions research, and then go on to discuss the DT framework and our approach to the analysis that follows.

'Energy transitions' is a broad and multi-disciplinary area of study. There is a plethora of different definitions and interpretations. In a discussion of the "emerging field of energy transitions", Araujo outlines a broad definition of the term: "a shift in the nature or pattern of how energy is utilized within a system", where "an energy system is a constellation of energy inputs and outputs, involving suppliers, distributors, and end users along with institutions of regulation, conversion and trade" ([36]: 112). Araujo continues that "change can occur at any level -from local systems to the global one -and is relevant for societal practices and preferences, infrastructure, as well as oversight" ([36]: 112). While some authors aim for more precision in defining energy transitions 1 , Sovacool concludes that "there is no standard or commonly accepted definition of an energy transition in the recent academic literature"( [37] : 205), but rather, there are different foci of analysis and conceptual tools which form the basis for differing perspectives.

Thus, rather than attempting to establish a strict definition, the key question is what perspectives are being used as an entry point to understanding energy transition phenomena and what particular discussions in energy transitions does the present analysis relate to. First, this paper relates to ongoing discussions on 'historic energy transitions' as Fouquet identifies [38] , which has seen more detailed examination of the historic factors influencing the speed and dynamics of transitions from the level of a single fuel or technology to the global scale [38] [39] [40] . Sovacool & Geels highlight that interpretations of historic transitions vary widely because there are different points of focal interest in terms of the 'multiple dimensions' of energy transitions [41] . This can include techno-economic analysis which primarily focuses on firms, sunk costs, investments, and the difficulties and long time-frames that energy transitions entail because of these economic factors, but also 'socioinstitutional analysis' which focus on political and policy interventions that influence past transitions and can trump these economic constraints leading to more rapid change.

A perspective that tries to bridge these 'multiple dimensions', and that Sovacool and Geels identify as "a key conceptual approach" in energy studies, is 'sociotechnical transitions' [41] . sociotechnical approaches focus on the co-evolutionary changes in energy systems and examine different elements including technology & science, markets & users, industry, institutions & regulations, where these different elements interact to form a 'seamless web' to deliver a particular societal function [42] . As Sovacool points out, many studies that take a sociotechnical perspective draw on the MLP which examines interactive developments between sociotechnical niches, regimes, and landscape pressures. A sociotechnical regime represents the dominant way of doing things, in terms of incumbent technologies and the rules and institutions that guide developments in an energy system. Niches, on the other hand, represent the level of novelty, innovation and experimentation [43] .

However, despite a plethora of work drawing on a sociotechnical perspective and the MLP, the 'landscape' level often remains underexamined in such accounts [15] . This includes wars, which in historic accounts drawing on the MLP are often used as temporal markers depicting discontinuity between different stages of development in energy transitions [22] , rather than focal points of analysis in their own right.

However, recently there has been increasing attention on world wars as a factor in energy transitions. For example, Samaras et al. [13] , in detailing the contemporary role of the US military in energy R&D around insulation and mini-grids, also highlight how strategic military decisions have shaped past energy developments such as the First World War transition of the British naval fleet to oil [13] . Matthew Evenden offers a detailed analysis of the ways in which Second World War mobilisation efforts in Canada played a decisive role in accelerating transitions to hydroelectric power under emergency measures to maintain adequate electricity supply to fuel industrial efforts for the Allied campaign [2, 5, 11] . More recently, Cohn, Evenden, & Landry conducted a historical analysis of Canadian, German and American mobilisation during the Second World War, and how this conflict played a crucial role in influencing the design of electricity systems in these countries [12] .

Of particular relevance to this paper, recent work by Ediger & Bowlus [4] moves beyond conventional commercial and technological factors outlining the importance of oil for military strategy in the build up to the First World War and its enactment, highlighting the central role of geopolitics as a driver of energy transitions. Rubio-Varas also focuses on the First World War, highlighting how disruptions caused by the conflict were decisive in influencing a rapid transition to oil that occurred in Latin America, decades before Europe [3] . The present work builds on and contributes to this sub-field, through engaging with the DT framework which we now discuss.

In this section, we discuss the DT framework, its constituent conceptual elements, what it is attempting to achieve and how it can be utilised to explore energy transitions. The framework builds an understanding of long-running developments in multiple sociotechnical systems across a 250-year period from the late 18th century and culminating in the post-war 'golden age' of economic growth and prosperity [15, 44] . The first deep transition is theorised as entailing four different 'great surges' of development across this period which constitute the slow building up of industrial modernity. The focus of the present work is on the 'fourth surge' which for Schot & Kanger represents the culmination of the first deep transition (Fig. 1) . The red circle in Fig. 1 highlights the fourth surge. Each surge constitutes a 'technological revolution' entailing a period of economic growth, based around a "…constellation of new inputs, products and industries, one or more new infrastructures -usually involving novel means of transport of goods, people and information-and alternative sources of energy or ways of getting access to it" ([45]: 4). The details of each surge are outlined in Fig. 2 .

For Perez, each surge follows a pattern entailing a period of 'irruption', where a number of new technological innovations emerge; a period of 'frenzy' entailing a battle between old and new technological configurations and economic paradigms; a period of 'synergy' where there is resolution and a particular new economic paradigm becomes stabilised; and then a period of 'maturity' where the particular paradigm and its constituent technologies and economic paradigms reaches saturation point, usually ending in crisis with the absence of new 1 For example, Smil outlines that an energy transition is the time that elapsed between the introduction of a new fuel and its rise to a 25% national or global market share [125] . Grubler, outlining 'grand transitions' as a new fuel reaching 50% market share [126] . Yet, these are not rigid definitions that should be adhered to, but particular definitions amongst a plethora of perspectives that constitute a varied and interdisciplinary field of research [37] . growth opportunities. These stages are outlined in Fig. 3 :

Although building on the 'great surges' approach, the DT framework differs in several important ways. First, the framework emphasises continuity across these surges, where the first four surges represent a single deep transition. Second, while Perez identifies a fifth surge based around Information Communication Technologies (ICT) with renewable energy as the key energy input, Schot & Kanger propose that this period instead represents the beginnings of a second deep transition. As they outline, "through gradual accumulation and coordination, niches may contribute to a fundamental overhaul of existing socio-technical systems, introduce a new set of sustainable and just directionalities… and thereby give rise to the Second Deep Transition"( [44] : 8). In this paper however, we are focused on the culmination of the first deep transition and more precisely, 'the age of oil' as depicted in the fourth surge. We do not discuss the second deep transition.

Second, the DT perspective posits that the drivers underpinning the emergence of particular surges can be understood from the perspective of the changing dynamics within sociotechnical systems. Innovation in niches is driven by system builders responding to particular problems in delivering societal needs and the search for solutions and improvements. The concept of rules discussed in the introduction, is used to understand how routines and behavioural patterns within sociotechnical systems influence path dependency and form sociotechnical regimes. Where the DT framework departs from most MLP-based analysis however, is it focuses on multi-system interactions and co-evolution, and how systems become increasingly aligned in a similar direction over time. That alignment process takes place when the same rule exists in multiple systems, referred to as a 'meta-rule'.

An important point to also note, recognised by Schot & Kanger and Perez, is that the time periods of surges strongly overlap. It is not the case that one surge disappears completely as another emerges. Due to issues including sunk costs and resistance from incumbents, there is considerable cross-over between surges as the elements of each surge are reconfigured and compete against each other until there is a resolution at a 'turning point'. With respect to the fourth surge and the question of energy, this relates to understanding how oil rapidly gained a significantly larger share of energy consumption in the years after the Second World War, in the USA, UK and Europe more widely, while the share of coal (the dominant energy source of the previous two surges) decreased [17] .

The present study focuses on the role of war in shaping this oil transition and how the rules of using oil and maintaining abundance and constant supply evolved in the context of the world wars. We now briefly discuss the approach taken to build our interpretive analysis.

In conducting our interpretive analysis, we seek to integrate geopolitical and historical accounts of oil developments in the twentieth century with a sociotechnical perspective. We focus on four different stages to frame our analysis based around Perez's depiction of the age of oil as including the stages of irruption (covering the time period of the First World War), frenzy (the interwar years), synergy (that includes the Second World War), and maturity (post World War II). In doing so, we are attentive to historical literatures which outline the key differences between the World Wars and peacetime in terms of the conditions of total war [46] [47] [48] . In conditions of total war, as Van Creveld writes, "war itself extended its tentacles deep to the rear, spreading from the trenches into the fields, the mines, and the factories" ( [34] , p.164). During periods of total war, entire economies and societies (rather than just a dedicated military as in other conflicts) are mobilised for the war effort [49] . Sociotechnical systems (including energy, food, mobility) become mobilised as part of a 'war machine' oriented around the single purpose of achieving wartime aims [50] [51] [52] . Multiple sociotechnical systems are reoriented from delivering civil societal functions to also supplying vast militaries.

A key mechanism of total war identified by Obinger et al is the immense demand-pressures that are placed on the economy entailing often unprecedented logistical challenges that can reorient patterns of production and consumption [53] . Building on the DT framework and the recognition of the key rule of maintaining abundant and constant supply during world wars [27] , we build on diverse literatures to build an interpretive account of how the exceptional demand pressures of total war influenced dynamics in multiple sociotechnical systems and the relevance these changes had for oil transitions. As Rip and Kemp outline, world wars provided a particular 'selection environment' for particular innovations and developments to 'break through' [42] . Thus, we focus on examples of strategic openings afforded for oil as a 'solution' to a variety of demand side challenges, as well as being attentive to evidence of potential destabilising forces with regards to other technological pathways [54] .

Obinger and Petersen also draw attention to the importance of the demobilisation phase, where soldiers and workers employed for war production have to be reintegrated back into civil economies [55] . This phase presents a particular economic challenge in warding off economic collapse once the demand-pull effects of war time cease and technological systems deployed in the war effort may also have to be reoriented back towards civil purposes. Also relevant in this phase are the legacies of war as a catalyst for change, where policies can continue into peacetime. Of particular relevance for our study and its focus on the USA and UK, are the legacies of policy diffusion and transfer which can be achieved in conditions of total war due to alliances between different countries and the effects of post-war reconstruction.

These mechanisms of total war provide a guide to shape our narrative analysis. In doing so the analysis is interpreted around the core rule identified by the DT framework of the imperative to use fossil fuels. Given our focus on the fourth surge and the recognition of the special importance of transitions from coal to oil during this period by Schot & Kanger [15] , for the purposes of the present analysis, we have refined this as the imperative to use oil. In integrating broad trends, geopolitical developments, and a focus on demand pressures in multiple systems, we respond to our overarching research question: what was the role of world wars in shaping the emergence of the age of oil in the culmination of the first deep transition?

In this section we outline our interpretive narrative of developments in multiple sociotechnical systems in four distinct periods, following the 'age of oil, automobile and mass production' identified by Perez. First, we look at events in the First World War in the UK and USA and identify broad trends and geopolitical developments before discussing illustrative examples of relevant developments related to energy, food, and mobility for considering oil transitions. We then discuss geopolitical factors related to USA-UK oil relations and sociotechnical developments in the 'frenzy' period between the wars. In the third part of our analysis we focus on the 'turning point' of the Second World War in the 'synergy' phase and in the fourth part, we look at the importance of post-war reconstruction efforts and the challenges of demobilisation. Drawing on literatures that analyse the role of the Marshall Plan in influencing technological developments in Europe, we critically assess the extent to which America's role in Europe shaped the wider diffusion of oil technology, infrastructures and governance.

We now discuss the First World War and developments relevant to oil transitions. We expand on the existing analysis of the role of the First World War on energy transitions [3, 4] through a focus on the multisystemic demand-pull factors that influenced the enduring 'thirst' for oil and related geopolitical developments [56] . We begin with a broad overview of trends and geopolitical developments before focusing on demand pressures and logistical challenges in energy, food, and mobility relevant to oil transitions.

Before the First World War the use of oil was limited with the main use being kerosene lighting [8] . In 1914 coal was still king. Oil provided under 5% of world energy supply while coal contributed to 74% [57] . In 1907, the value of the UK's coal trade surpassed £52 billion, while the total value of all petroleum exports from the USA amounted to some £19 million [57] . Yet the First World War was a significant rupture in this pattern of development as global use of petroleum grew by 50 percent while coal production decreased in many European countries [8] . In the century prior to the war, British geopolitical dominance was secured by its steam-powered navy, and at the turn of the 20th century, the UK was the world's leading energy exporter [58] . However, the First World War interrupted this trend and concerns about access to oil would be key to these changing geopolitical dynamics [10] .

The UK faced a central challenge during World War I as it had limited reserves of oil. During the war, 90% of the oil required for the British as well as French war effort was supplied by the USA [57] . The UK (along with France and Italy) became dependent on the USA to fuel their military efforts during this increasingly oil-intense conflict. These dynamics intensified with the oil crisis of 1917 where, due to the everincreasing amounts of oil being consumed by militaries in Europe and the disruption of oil supply routes by German submarine attack, there were significant risks of oil supply running out. Influenced by these intense pressures, the USA, UK and other countries, including France and Italy, were drawn closer together by the imperative to maintain constant supplies of oil. As Yergin points out, the oil crisis caused by the First World War forced the United States and its European Allies into tighter integration of supply activities [7] . Geopolitical tensions increased in the Middle East driven in part by the search for oil, with Britain attempting to gain control of important oil fields in Iraq. The Sykes-Picot Agreement signed in 1916 by the UK and France carved up Mesopotamia between the two countries and is understood to have been partly influenced by desires to secure strategic oil resources [59, 60] . As several authors point out, the First World War and the thirst for oil amplified the geopolitical significance of the Middle East, leading to increased tensions between the USA and UK (along with France) after the war [4, 7, 33, 61] .

But these broad changes and geopolitical developments to secure oil resources were rooted in specific sociotechnical challenges driving the increased demand for oil in energy, food, and mobility. We now explore the demand pressures and logistical challenges caused by conditions of total war and the implications for oil transitions.

In the years preceding World War I, the advantages of oil ships had been recognised by many navies around the world. The advantages of oil included the fuel being double the thermal content of coal meaning less space was required for storage; logistics of refuelling at sea were therefore made easier; reliance on docking stations for refuelling was reduced; and there was greater flexibility in changing speeds as well as less personnel required on ships [62] . Additionally, oil-based ships produced less smoke which was beneficial to gunnery operations and enabled more covert movements of naval fleets [63] . An early adopter of oil-powered ships was the British Navy. The share of oil-based vessels in the British navy rose from 5% at the start of the war to over 40% by the war's end [7] 2 . Prior to World War I, most shipping was steampowered, and thus the application of oil to navies was a key niche development supported by the military and accelerated by the First World War. During the conflict, the US navy which had already converted several ships from coal to oil accelerated this trend [7] . Germany, on the other hand, did not use all-oil firing for surface fleets until after the war [63] .

Internal combustion engine-based automobiles and trucks were a niche in the mobility system before the war. However, they became increasingly used for tactical advantage during the war by the UK and USA as significant problems were experienced with rail road transportation. The First World War has been described as the pinnacle of the 'rail age' [64] dependent on coal, yet significant disruptions occurred with railroad bottlenecks on the Western Front disrupting the supply of weaponry and materials to troops. In Allied campaigns such as the battle of Verdun, the rapid construction of roads and use of motor vehicles for transportation further entrenched the importance of oil for military victory [65] . An example used by historians to exemplify a general point about the greater military dependence on the automobile and trucks is that at the beginning of the war the UK military had 823 automobiles and 15 motorcycles. By the war's end they had 23,000 motorcars, 63,000 trucks, and 34,000 motorcycles [7] . Away from the front, in the USA, railroad arteries were also blocked and, under the auspices of the US High Transport Committee, caravans of trucks carrying important goods for the front line were initiated, "inaugurating the long-distance trucking of freight as an alternative to rail transportation and calling attention to the great need for a national system of interconnected, improved highways" ([66]: 78).

During the conflict, a new reality of 'war from the air' emerged. The aeroplane, which was in its 'embryonic phase' as a niche technology at the start of the war, had consolidated as a major industry by the war's end increasing requirements for gasoline products [67] . In Britain, as Edgerton outlines, this created a very large aircraft industry, with increases in output accelerating through the war. Monthly output increased from about ten per month at the war's beginning to 122 in 1917 and 2,688 in 1918. The number of people working in the UK's aircraft industry rose from nearly 49,00 in October 1916 to 154,000 in November 1917 to 268,000 in October 1918 [68] . In the USA, there was also considerable aeroplane construction with 10,000 constructed by the war's end [8] . This created a surplus of aircraft after the war. As Responses to demand pressures in the food system also had 2 The decision had been made by Winston Churchill in 1911 to transition the entire British fleet from coal to oil and this is cited by historians to exemplify the general point concerning the greater dependence of militaries on oil emerging during World War I [7] .

implications for oil supply. Food imports became significantly disrupted and blockading food supplies became a key strategy of both the UK and Germany during this war. Thus, a focus on 'self-sufficiency' intensified in the UK [69] . There is evidence that the First World War also led to niche experimentation to maintain agricultural supply in response to these demand pressures. Coal and steam power had not made significant inroads into the agricultural sector and farming was still mainly reliant on horse power. However, the First World War accelerated the development and marketing of tractors [70] . In the UK in 1917, the Government ordered 400 British Saunderson Tractors and $3.2 million was invested in US models such as the Fordson. Ford exported 7,000 tractors to Britain in an effort to boost agricultural productivity [71] . In the USA, tractor use also expanded under government loan schemes and propaganda campaigns with expos being used by government to further encourage their use [72] .

We now discuss both broad geopolitical developments and relevant sociotechnical developments with regards to the inter-war years and oil transitions.

The First World War created an 'oil frenzy' which significantly influenced international relations after the war [57] . The 1920s can be considered as a period of international instability with respect to global oil supplies as the heightened recognition of the strategic importance of oil created tensions between different nations. As Black notes, the First World War and the emergence of oil as a 'strategic resource' [73] meant that "…new systems of negotiation and need had emerged that would eventually be referred to as "geopolitics." ( [8] : 140).

Before the First World War, Britain controlled only 5% of the world's oil production, but by the war's end Britain had acquired 50% of the world's known oil reserves [74] . France and the UK struggled for control over Middle Eastern oil resources, and in April 1920 the San Remo Agreement was reached between the two countries. Here, "Britain conceded a share of the oil in exchange for a general agreement, effectively granting France a 25 percent share of petroleum in exchange for Mosul" ([59]: 41). This locked out foreign companies from being able to control oil production in the British Empire. The USA retaliated with similar measures, using the Mineral Leasing Act of 1920 to prevent any company from a nation that was excluding American oil companies in the Middle East from gaining access to US oil fields. New oil discoveries in Texas in 1924 eased this geopolitical tension. However, the new thirst for oil and wartime experiences of oil shortages had resulted in an 'exploration boom' [7, 75] . This led to low prices which risked the stability of the global oil industry.

The 'Red Line' Agreement at Achnacarry in 1928 sought to control global oil prices and form monopolies around oil access. The agreement saw the creation of the 'Seven Sisters' oil cartel where agreement was reached to cease independent prospecting for oil in the Ottoman empire by individual oil companies and instead conduct coordinated explorations as a cartel [76] . This agreement was an attempt to create stability in the global oil regime, yet tensions between the United Kingdom and the USA continued as Britain pursued a strategy of trying to secure its oil resource independently from America [7, 10] . However, Britain did not have the industrial capacities to exploit significant amounts of oil in the Middle East, and the USA maintained its focus on exploiting indigenous oil reserves.

It is worth pointing out that the UK's strategy for oil independence differed in the inter-war years from Germany in significant ways which would ultimately have implications for World War II. Germany was economically and politically weakened after the First World War and could not acquire oil reserves. A key part of their strategy was to pursue petroleum synthesized from coal [10] . Germany established a synthetic fuels industry to meet the rising demand for oil as the country continued to industrialise during remilitarisation in the 1930s. The energy intensive process of producing synthetic oil from coal would also ensure that territorial expansion to acquire resources of crude oil would be key to German military planning and strategy in war [10] . The oil strategy of the UK also had its limitations during this period of 'frenzy' however. The UK put considerable effort into securing Middle Eastern oil supplies, and while in 1929 the USA produced more oil than any other country, 41% of oil production outside of the US was produced by British companies [10] . However, this strategy proved flawed in the build up to the war as routes through the Mediterranean were hampered by Italy in the 1930s. Britain could not secure its supply routes and did not have adequate tanker capacity to transport the oil.

The imperative to maintain a constant supply of oil amplified by World War I had accelerated production in the US oil industry and this presented the challenge of re-orienting to peacetime activities. As Auzzanneau writes "unable to settle down and smoothly adapt its production to the new conditions of peace, the oil industry experienced an intense overproduction crisis after 1918" ([76]: 100). Yet, oil production and consumption continued to steadily increase in the USA, with the rise of car culture and mass consumption during the 'roaring twenties'. However, in the UK this expanse was more modest. Despite being adversely affected by World War I and facing significant economic problems, rail in the UK was not challenged by road transportation to the same extent as in the USA and its 'clash of cultures' between the automobile and rail systems in the inter-war years [77] .

The significant wartime problems of bottlenecks in flows of truck freight resulting from poor road infrastructure experienced during the war gave impetus for mapping out and then funding improved road infrastructure in the USA. The Federal Highway Act 1921 to construct a joined-up road network linking US cities was unveiled specifically citing military considerations as a reason to invest in highway construction [78] . In the UK, the Ministry of Transport was established in 1919 and introduced a national system of road signage, a system of grants for local authorities to construct roads, and set up a research laboratory to investigate matters of road construction [79] .

Several authors conclude that while WW1 had been an accelerating force for oil, coal had been negatively affected by the conflict, including through infrastructural damage, depleted labour supply and labour strikes [4, 57, [80] [81] [82] [83] . According to the official history of the British coal industry for example, British coal was an 'industry in decline' after the First World War [83] . This is reflected in the writings of Trade Unionist Ivor Thomas, who in 1934 lamented this decline stating that "whether we like it or not, we are entering -or have indeed entered -an oil age" ([84]: 43). Yet in the UK, the coal industry remained powerful and what was referred to at the time as the "back-to-coal" lobby still had considerable influence ([84]: 43). 3 Another impact of war relevant to oil transitions, was the emergence of new users capable of operating automobiles or aeroplanes as a result of their wartime experiences. The war popularised a product that had heretofore been viewed as elitist. Automobiles, for example, moved from being niche vehicles to a more familiar form of transportation [65] . The military surplus of aeroplanes created by World War I was also significant for post-war developments in the USA: some of the 10,000 planes that had been constructed were integrated into civil aviation which was being utilised for activities including mail delivery [67] . While tractors continued to be used on both sides of the Atlantic, growth was modest in both countries [68, 71, 84, 85] , although in the USA, the use of tractors increased through support for agriculture under the New Deal in the 1930s. However, it would be during World War II that the 'petrolification of agriculture' [86] would take place, as well as acceleration and innovation in the oil industry leading to the further embedding of oil in the mobility system.

We now focus on the Second World War, again summarising broad trends and geopolitical developments before discussing relevant sociotechnical developments with regards to the conflict.

The Second World War was a global conflict with a marked increased dependence on oil compared to the First World War. For example, American forces in Europe used one hundred times more gasoline in World War II than in World War I [7] . Two years into the war, in 1941, oil supplies to the UK became cut off as a result of German submarines attacks [88] meaning that as the war progressed, a key challenge became sustaining constant supplies of oil to Europe from the USA [7, 33, 89] . As this challenge was met, the war transformed patterns of energy imports and exports across the transatlantic zone. Before the Second World War, the UK was still one of the world's main energy exporters. Britain's increasing reliance on the United States for supplies of oil that emerged over the course of the First World War had dissipated, and instead the UK sourced much of its oil during the inter-war years from countries including Venezuela, Dutch West Indies, Iraq, and Persia. However, shipping routes from these regions were disrupted during the Second World War. As Edgerton points out, even as late as 1940 the British were determined to maintain their oil independence from the USA [90] . Yet, as the war progressed the UK became reliant on the US for 90% of its oil supply, paying for it with assistance through the Lend Lease Programme [91, 92] .

During the course of the war, the USA began turning attention towards securing future supplies of oil for future wars and projected increases in demand in post-war society [76] . In 1944 American Geologist Everytt Gower returned from Saudi Arabia to announce that the oil in the region was the "greatest single prize in all history" (quoted in Yergin [7] : 393). Negotiations between Roosevelt and Churchill took place regarding this future oil supply near the war's end. In secret meetings at the Suez Canal between Roosevelt and Abdul Aziz ibn Saud however, it was established that Britain would not gain control over Saudi's oil reserves and that Saudi would exist in the American sphere of influence [76] . This moment and subsequent agreements would be decisive in fundamentally altering international energy trade and geopolitics.

It is also worth pointing out, that oil had a far stronger influence on war strategy during this conflict. Due to its lack of indigenous oil resource and dependence on synthetic fuels derived from coal, Germany sought to acquire oil resource through territorial expansion. The German quest for oil in the Caucuses is identified as a motivating factor in the invasion of the Soviet Union for example [9] . The Allied Oil Campaign put significant resource into destroying German oil infrastructure and refining capacity [10, 76, 93] . Waging war was now dependent on oil resources with global networks of shipping routes and refineries extended as the Allied campaign sought to acquire and deliver adequate oil supplies to multiple theatres of war.

We now look from a sociotechnical systems perspective at the specific demand pressures and logistical challenges that were accentuating the imperative to use oil in the energy, food and mobility systems.

During World War II the construction of oil infrastructure was rapidly accelerated. In the USA, the 'little inch" and "big inch" pipelines were constructed in under a year, between 1942 and 1943, as a means to transport oil across the US from the South to the North East [94, 95] . At the start of the twentieth century, pipe size had been standardized at eight-inches, however this could only move 125,000 barrels a day even though a refinery could produce up to 125,000 barrels. As Richard Rhodes points out, solutions in the form of wider pipes and 'looping' techniques were already developed but private companies were not prepared to make the requisite investment. However, during the war these innovations in pipeline technologies were put to use. As Johnson notes, "in the endeavour to meet the demand for crude oil and petroleum products on the East Coast, government-financed pipelines embodied technological innovations -particularly with respect to diameter of pipe -that were to have a lasting impact." ([95]: 78). The "big inch" and "little inch" pipelines stretched for 1,254 miles across the USA with pumping stations every 50 miles. The 'Big inch' pipeline was capable of moving 350,000 barrels of crude daily and it was, at that time, the largest and longest pipeline ever built up [94] . An Industry Pipeline Management Committee oversaw the expansions of pipelines under the 'Tulsa Plan' and over 3,200 miles of new pipeline was dug and laid during World War Two in the US to enable meeting the vastly increased demand during wartime [91] .

In the UK, due to the threat of aerial bombardment of road infrastructure as a means to transport oil, construction began on the Government Pipelines and Storage System (GPSS) in 1940, with the first phase completed by 1942. The system connected key locations such as Liverpool docks with Avenmouth through underground pipelines stretching for 220 km. In 1943 the pipeline system was extended to connect up various airfields in the East of England. As the GPSS system was extended further, this network of pipelines would eventually supply aviation fuel to all of England's air fields [88] . This was a significant technological breakthrough given that there was little knowledge of pipeline construction in the UK prior to the war [88, 96] .

Innovation in the oil sector was stimulated by the changing demand pressures and logistical challenges of war. World War II is referred by some historians as an 'air war' [97] or 'the bombing war' [98] and during this conflict the aircraft industry was transformed. Innovations in oil production methods, including perfecting 'catalytic cracking techniques', made possible the production of large volumes of 100-octane gasoline [7] . This fuel was in high demand from the once burgeoning and now mass-producing aircraft sector, with oil intensity increasing as jet engines and four engine bombers were developed. Huge refineries were rapidly built to facilitate the increasing demand for different types of fuel [87] . While 100-octane gasoline and associated innovations were developed before the war there had been no market for them prior to the conflict [99] .

With the 'mass mobilisation of science' during World War II [100] , a host of other scientific endeavours led to the rapid expansion of the aero-industry further entrenching a reliance on oil. This included advancements in radar technologies, air precision, electronics, computing, and cabin pressure. Meanwhile the US auto industry was redirected towards the war effort and played a central role in the mass production of tanks, trucks, jeeps, aeroplanes, bombs, torpedoes, steel helmets and ammunition under huge contracts issued by government [50, 92, 101] . The British car industry was similarly re-directed towards the production of war materiel [102] . This mass mobilisation of the auto-industry for the war effort would see the sharing of innovation and collaboration around mass production techniques with significance for increased post-war production of automobiles [101] [102] [103] In the food system, the immense pressures on agriculture to increase production in the USA and UK, accelerated the mechanization of agriculture, including the increased use of tractors and combine harvesters. For example, in 1939 there were 56,000 tractors in the UK, by 1940 this had risen to 100,000 [69] . In the USA, the number of tractors on farms rose from almost 1.6 million tractors in 1940 to 2.4 million tractors in 1945 -an increase of two-thirds. Innovations took place in the design of tractors as they were mass produced: tractors got smaller, hydraulic systems were introduced, and they became more powerful. The energy intensity of US agriculture also increased and new innovations such as 'hybrid corn' and larger farm sizes accentuated the need for pesticides and insecticides which were also being rapidly developed during the war to protect troops fighting in the Pacific from disease [87] . Some plant protectants developed during the war were dependent on the petrochemicals industries that were consolidating as the refining of oil increased during the war [87] . These changes in agricultural practices occuring during the war were wide-ranging and were rapidly adopted. As Rasmussen writes, "higher prices and a seemingly unlimited demand for farm products, combined with a shortage of farm labor and appeals from the government to increase production, led farmers to adopt technological advances" ( [86] : 588). These advances entailed increased "input of mechanical power and machinery, fertilizer and lime, chemicals, feed and seed, and other items" ( [85] : 588). Thus, an increasing thirst for oil in the food system was generated by these developments.

The development of plastics from petrochemical sources was also accelerated during the Second World War in the USA, and would have important implications for the food system in the post-war era. In 1937, the first meeting of the Society of Plastics Industry (SPI) concluded that there was no market for these products [104] . However, during the war, demand pressures meant there was an urgent need to conserve aluminium, copper, steel and zinc for war materiel. These pressures, combined with increased oil production during the war, meant that an opening was created for oil-derived products to act as substitute for scarce resources and were used in clothing as well as acting as a solution for food preservation and storage. Between 1940 and 1945 production of plastics almost tripled in the USA [105] . As Black notes with regards to the burgeoning plastics industry, "petroleum became a primary component in allowing producers to overcome limits of supply and production" ([106]: 44).

Towards the war's end, the new condition of future US energy policy was stated by the State Department's Petroleum Advisor: "[the central objective] …is not a rationing of scarcity, but the orderly development and orderly distribution of abundance." (Quoted in Yergin, [7] : 401). In 1951 Oil surpassed coal as the main source of energy in the USA [107] . The Second World War had been key in transforming the infrastructure associated with oil, and much of this had been achieved through government spending. After the war, the US government set about transferring government holdings of pipelines refining capacity and tankers to the private sector [91] . Post-war lobbying by the US coal industry to close the 'little inch' and 'big inch' pipelines on the basis they put the coal industry at a competitive disadvantage failed [94] , and these pipelines open up East Coast America to increased supplies of oil as well as natural gas [94, 108] . In 1945, after the Japanese surrender, oil rationing was suspended in the United States and the stage was set for consumers to "…design[…] their post-war lives around energy decadence" ( [8] : 143).

In the USA, a key challenge for the post war period, according to Bonneuil & Fressoz, related to the immense productive forces that had been mobilised during total war and the "…problem of productive overcapacity and its reconversion into peacetime" ( [87] : 145). The automobile industry stabilised and set about producing cheap cars in record numbers, thereby sustaining the levels of high employment achieved in the war years and working with newly refined mass production techniques perfected during the war [101, 109] . The highway expansion programmes of post-war America enabled a further rapid acceleration of the automobile culture and -similar to the programmes after World War I -were influenced by military as well as civil requirements building on wartime proposals set out by Roosevelt in 1943 and the Highways Act 1944. The Second World War had also transformed air infrastructure: the wartime development of a network of runways equipped with new air traffic control systems and standardised aircraft paved the way for the rapid expansion of domestic and international aviation.

Oil flowed through the food system in different ways, with plastics increasingly used in food packaging and preservation [104] . The mechanization of agriculture accelerated during the Second World War continued to expand in peacetime and required increasing amounts of petroleum to power industrial farming [110] . Additionally, the transportation of agricultural produce by truck became more widespread as large highways systems were constructed [78] . Oil had seeped into every part of American life, forming what Black refers to as a "ecology of oil" [106] . Here, "oil does not just fuel Americans' vehicles. Oil has changed their diet, their clothes, their neighbourhoods, their jobs, their fun-in fact, everything about U.S. society" ( [106] : 41) .

The situation of extreme scarcity caused by the tragic destruction of war experienced by continental Europe after World War II was very different to that of the United States. Production of coal had fallen in the UK and across Western Europe and coal infrastructure, especially in Germany, had been damaged [31] . Traditional trade routes and supplies did not return to normal immediately after the war and the industry was in a state of crisis [111] . Although the UK had not been as badly affected as countries on the continent, there were still grave concerns about the depleted coal industry [112] .

The UK was now a net energy importer, and set about attempting to reconstruct its industries through nationalisation [113] . Yet, in the early 1950s, the UK's share of oil began to rise markedly, reaching 12% in 1955 from a share of less than 5% at the war's end [31] . This trend continued and the UK's imports of oil rose rapidly through the 1950s. in 1939 the UK imported 2,201 thousand tonnes of oil. In 1946 the UK imported 2,214 thousand tonnes [114] . But by 1953 this had increased over ten-fold to 23,063 thousand tonnes, increasing year upon year to a historic maximum of 115,472 thousand tonnes in 1973. Despite attempts to gain control of oil in the Middle East after the Second World War, the UK's oil imports were largely from Middle Eastern supplies under the sphere of influence of the USA [32] .

The outcomes of the Second World War and the nature of reconstruction have been identified by several authors as important factors influencing a rapid transition to oil that occurred across Western Europe in the 1950s [38, 107, 115] . The 'black gold' of Saudi Arabia, controlled by the USA, was not used initially to fuel American abundance but rather to facilitate the reconstruction of Europe. Thus, the solution to the problem of European energy scarcity was, to some extent, American abundance. The European Recovery Programme (Marshall Plan) was initiated by the USA in 1948 and 10% of Marshall Plan loans related to the importation of oil to Europe [91, 116] .

The share of petroleum products in the primary energy consumption mix of Europe at the end of the war was around 10% [31] ; by 1955 it was 21% and by 1964 it was 45% [31] . In the 1950s several pipelines were built connecting Europe to Mediterranean supply routes from the Middle East and extensive networks of pipelines were built across Europe including the TAP line completed in 1950, Inter-Provincial in 1950, and the Trans-Mountain in 1953 [31] . As historians of European infrastructure point out, these European pipeline projects drew on successful wartime experiences with constructing extensive pipeline networks such as the GPSS in the UK [117] .

Historians highlight that the European oil transition was fundamentally shaped by the USA's new-found global dominance and Cold War concerns about Europe becoming dependent on oil from the Soviet Union. As Boon writes, after the war "neither a distinct Western European Oil regime nor an integrated [European Economic Community] governance framework for energy materialised", rather, "…the transition to oil evolved under a global regime dominated by multinational oil companies -then at the apex of their power and closely linked to the informal empires of the US and Britain" ( [118] : 83). In short, the age of oil in Europe was strongly facilitated by innovations and frameworks amplified during the war in the USA that diffused to the European context as oil companies constructed pipelines and refineries underpinning a rapid transition to oil.

The oil dependence of Europe grew as the restoration of Europe's transport infrastructure took place, particularly evidenced by increases in road mobility, automobile ownership, and trucking. There is evidence of the USA's preference for exporting trucks to Europe rather than rail freight after the war, and strong lobbying by the US to push for prioritisation of road construction in Europe's infrastructural recovery [119] . As Seely highlights, "…the relative ease with which Americanstyle highway and traffic engineering moved across the Atlantic also was a product of the willingness-indeed eagerness-of American engineers, government officials, and industrial leaders to assist in this diffusion process" ( [120] : 230-231). Similarly, with regards to the food system, the Marshall plan is also a relevant factor to consider. The technological transfer of tractors, industrial agricultural techniques, hybrid corns requiring fertilisers and other plant protectant innovations to the UK and other Western European countries was faciliated through agricultural support mechanisms as part of the Marshall Plan [121] .

The emergence of the USA as a superpower during the Second World War as the UK's geopolitical power diminished, therefore seems relevant to understanding the rapid diffusion of the imperative to use oil to Europe after the conflict. The oil intensity of the US had increased markedly in multiple sociotechnical systems particularly as a result of rapid developments that had occurred in response to demand pressures in the Second World War, and the embeddedness of oil in multiple sociotechnical systems underpinned a new society based on abundance, influencing the nature of the European recovery through the Marshall Plan.

We now discuss the significance of our interpretive analysis in terms of the role of war in energy transitions, and the contribution the present work makes in responding to and developing the DT framework. We also discuss the value of the DT framework for energy transitions research.

Focusing mainly on the USA and UK, we have conducted an interpretive analysis of the world wars and the emergence of the oil age, integrating insights from geopolitics and historical literatures with a sociotechnical perspective on multi-system demand pressures. Under the exceptional demand pressures of total war, the imperative to maintain abundance and constant supply saw the search for solutions to meeting demand challenges, and in both the First and Second World Wars this process deepened society's reliance on oil resources. The imperative to use oil was thus accentuated in multiple sociotechnical systems during war time. With regards to World War I, our analysis corroborates work in energy transitions that has interrogated the key role of the conflict in influencing a shift from coal to oil, where war can be seen as an extreme form of 'creative destruction' [4] . The present work also chimes with studies of the role of war on energy transitions including hydro-electricity in Canada, the USA, and Germany [2, 5, 11, 12] that highlight the importance of world wars as mobilising forces for energy transitions.

Given the limitations of our geographical focus, our broader conclusions on the role of war in energy transitions must necessarily be cautious. Indeed, the pattern of the emergence of the 'oil age' at the global level does not necessarily fit the time period of the 'fourth surge' as depicted by Perez. As Rubio-Varaz highlights in an analysis of Latin American transitions to oil influenced by the First World War, these occurred at a far earlier stage than Europe [3] . However, the stages of the 'age of oil' in terms of irruption, frenzy, synergy, and maturity fit with the developmental processes with regards to the USA, UK and Western Europe.

With the existing work on energy transitions and world wars in mind, the present analysis can be used to draw out propositions about the role of war in energy transitions and the mechanisms that influence energy transitions. These are not designed as definitive conclusions but rather insights from the present research that could be tested further with different case studies, national contexts, and international dynamics contributing to the emerging literature on world wars and energy transitions. We outline three propositions as follows:

1. World War amplifies both 'sides of the coin' of sociotechnical transitions. Kivimaa and Kern [54] refer to the creative processes of sociotechnical niches being nurtured and the flip side of destabilisation of existing regimes as both being crucial in understanding transition processes. In this study, the demand pressures of war, and the search for solutions to these problems, saw a range of developments taking place during wartime that further embedded oil in multiple systems. This included the acceleration of automobiles and aeroplanes in the First World War, increased mechanisation and tractor use in response to labour shortages in the First World War, and petrochemical solutions to shortages of materials in the Second World War. These technologies and innovations existed prior to the wars, however strategic opportunities for their use were opened up by the particular selection environment of wartime. At the same time, the coal industry, and associated industries in the mobility sector experienced destabilising consequences both in the First World War, which was compounded by the World War II, due to severe disruption of export routes, infrastructural damage, and labour shortages.

This at first seems counter-intuitive because war is of course divisive, and considerable literature has rightly drawn attention to the tendencies towards a push for greater national self-sufficiency and autarky in energy as a result of war. This is certainly true in some respects, however in the case of oil we see that the UK and other European countries became more tightly bound to the American oil regime during the First World War through the Inter-Allied Petroleum Conference. While in the period of 'frenzy' the UK attempted to forge its own path, the integration between the US and British energy systems intensified once again in the Second World War. Through re-orientation and reconstruction, the post-war period saw this integration continue as the UK, along with many Western European countries, transitioned more rapidly to become embedded in a 'global' oil regime largely controlled by the United States.

surplus and reconversion. The foundations of the oil-based society were laid during the Second World War. Extensive pipelines in the USA and the UK built to fuel the war effort were reconverted to supply oil and natural gas to the American East Coast in the case of the USA, and aviation fuel to airports for civil aviation in the case of the UK's pipeline developments. Runways, air traffic control systems, and streamlined global logistics networks shaped during World War II for air transport were reoriented to civil aviation. The surplus of agricultural produce in the United States had to be maintained in order to ward off economic collapse and petroleumreliant industrial agricultural practices persisted and intensified to maintain this abundance. After the First World War, a surplus of planes in the US and UK were absorbed into civil airlines, then in their infancy. The First World War created hundreds of thousands of new users of oil-dependent automobiles and aeroplanes.

In addition to these points, the role of war in energy transitions can be further explicated by returning to the implications of this analysis for the DT framework.

Through a focus on the demand pressures of world wars and the solutions that emerged to these challenges, our analysis has highlighted how in these wars the imperative to use oil was accelerated in the energy, food, and mobility systems by innovations and experimentation where reliance on oil was often a key solution. The three systemsenergy, food, and mobility -became more tightly integrated as a consequence of wartime activity. Following Schot & Kanger, we have contributed to the DT framework in terms of "understanding how changes across multiple systems became connected and coordinated, developing a common directionality in the long run" ( [15] : 1046).

While the trend towards oil use accelerated faster in the mobility system after World War I and the growth of mechanised agriculture was modest, during World War II these systems become even more tightly integrated. Pipeline infrastructure, refinery capacity, petrochemicals, plastics, pesticides, increased mechanisation of agriculture, mass production of aeroplanes, construction of runways, and a host of other concurrent developments were accelerated by war. In the language of the DT framework [15] , the role of war in deep transitions is the tighter integration and coordination of multiple sociotechnical systems in a similar direction. The world wars amplified the meta-rule of the imperative to use oil, and shaped the sociotechnical conditions to deliver abundant oil supply in numerous domains.

More broadly, we argue that the DT framework can be a useful conceptual tool for energy transitions research. In focusing on multiple rather than single systems, the DT perspective analysis of the age of oil conducted in this paper, reveals the interdependencies between different systems and how they are tied together by oil infrastructure and use. These multi-systemic understandings can be of value in thinking about the shift away from an oil-based society, and the need for multiple policy interventions and policy mixes to enact a deep energy transition based around sustainable sources of energy. The focus on rules and meta-rules can assist in enhancing understandings of how broader transitions beyond one sociotechnical system occur and shine a light on the more deep-rooted unsustainable routines and patterns of behaviour associated with the age of oil that must be undone if more rapid sustainability transitions are to occur.

With its focus on exogenous events like wars, The DT framework can also be utilised to explore mechanisms for deepening and accelerating renewable energy transitions beyond niche-regime dynamics, and the multi-system interactions that may need to be fostered if an 'ecology of renewable energy' rather than oil, is to be achieved. This highlights the value in further interrogating other 'landscape' events that could be influential in the directionality of renewable energy transitions. For example, the particular demand pressures of the COVID-19 pandemic has had a significant impact on energy systems that could be decisive in shaping lasting change [122] . Additionally, the DT framework's attention to military and wars and their historic role in accelerating particular transitions, also emphasises the importance of considering mobilising forces that can also decisively and rapidly influence the directionality of energy systems but that are not reliant on the tragedy and violence of war. Indeed, given the enduring links between militaries and unsustainability [123] , a key question for sustainability transitions scholars is the extent to which rapid low carbon transition is feasible if current systems of defence, violence, and militarisation remain in place. This points to forms of 'deep incumbency' including the military that warrant more dedicated attention [124] .

In this paper we have focused on the emergence of the age of oil in the twentieth century which forms the culmination of the first deep transition. We have conducted an interpretive analysis drawing on geopolitical and historical literatures to build an understanding of how the exceptional wartime demand pressures and logistical challenges experienced in multiple sociotechnical systems influenced oil transitions.

The role of the two world wars in shaping the emergence of the age of oil in the culmination of the first deep transition can be summarised as follows: the exceptional conditions of total war saw the imperative to use oil being accentuated in multiple sociotechnical systems. As a consequence of war time pressures, energy, food, and mobility were coordinated in a similar direction through the meta-rule of using oil, and became more closely integrated based around an increasing dependence on oil. Wars saw the rapid development of the technological, infrastructural, logistical, scientific, and institutional conditions underpinning oil-intense societies of the post-war economic 'golden age'. Thus, the two world wars were decisive in shaping the directionality of the culmination of the first deep transition.

The present analysis suggests that war, often discussed in MLP approaches as a residual landscape factor rather than a focal point of analysis, has an important role in shaping historic sociotechnical transitions. Going forward, energy and sustainability transitions research could further unpack the landscape category examining the dynamics and mechanisms that different kinds of landscape shocks entail and the implications for sociotechnical transitions. It seems apparent that military activities and wars were influential drivers ofhistoric carbonintense and environmentally damaging energy transitions. Looking towards the prospects for a second deep transition, it may be that processes of peace-making and demilitarisation deserve a more central role in ongoing struggles for a sustainable future.

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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The Army and Economic Mobilization (United States Army in World War II: The War Department), Centre for Military History USA

Strategies for Rapid Climate Mitigation: Wartime mobilisation as a model for action? Routledge

Introduction: Studying the Welfare-War Nexus

Creative destruction or mere niche support? Innovation policy mixes for sustainability transitions

Mass Warfare and the Welfare State -Causal Mechanisms and Effects

How World War I ushered in the century of oil

The Political Economy of World Energy

Steam Power and Sea Power: Coal, the Royal Navy, and the British Empire, c. 1870-1914

France's Middle Eastern Ambitions, the Sykes-Picot Negotiations, and the Oil Fields of Mosul

The First World Oil War

Coal and the Advent of the First World War at Sea

Naval Innovation. From Coal to Oil

War by Timetable: How the First World War Began

Atlantic Automobilism: Emergence and Persistence of the Car 1895-1940

The Automobile Age

Turbulent Skies: the history of commercial aviation

England and the Aeroplane

Food for War: Agricutlure and rearmanent in Britain before the Second World War

Output and technical change in twentieth-century British agriculture

American agricutlure in the twentieth century

The emergence of strategic resources in world politics: A study of Petroleum and the international system

Oil, war, and American security: the search for a national policy on foreign oil

Oil Power and War: A Dark History

Clash of Cultures: road versus rail in the North Atlantic World during the interwar coordination crisis

Federal aid to roads and highways since the 18th century: A legislative history

What Went Wrong ? British Highway Development before Motorways, Motoring towards 2050 -Roads and Reality Background Paper

Toward a Sustainable Energy Regime

Global Energy Shifts

Carbon Democracy: Political power in the age of oil

Problems of the British Coal Industry between the Wars

Coal in the new era

The Impact of Technological Change on American Agriculture

The Agrarian history of England and Wales: Volume VIII

The shock of the Anthropocene

Pipelines and PLUTO: A History of the United Kingdom's Largest Oil Pipeline and Storage System during World War Two

The history of the European oil and gas industry (1600s-2000s)

Warfare State: Britain

The American petroleum industry volume II: The age of energy 1899-1959

Freedom's forge: How American business produced victory in World War II, Random House

Why the allies won

Energy: A Human History

Petroleum, pipelines, and public policy

Oil: A study of war-time policy and administration

Air Power in the Age of Total War

The Bombing War: Europe 1939-1945

History of Aviation Part Three: World War II through 1980's, Covingt

Science in the Twentieth Century and Beyond

Automobile Manufacturer's Association, Freedom's Arsenal: The story of the Automotive Council for War Production

Mot. Pop. Cult, 20th Century

The Automobile Industry and the Coming of the Second World War

By Design: World War II, plastics, and

Legacies of War: How the Commercialization of Plastics in the United States Contribute to Cycles of Violence

Oil for Living: Petroleum and American Conspicuous Consumption

Energy at the crossroads: global perspectives and uncertainties

The Car Culture

The 20th century transformation of U.S. agriculture and farm policy / Carolyn Dimitri

Power to the People Book: Energy in Europe over the Last Five Centuries

Electricity before Nationalisation

War and the Development of the British Welfare State

Energy transitions

The Marshall Plan and oil

Europe's Infrastructure Transition

Multinational Business and Transnational Regions: A transnational busines history of energy transition in the Rhine region

Changing the face of Europe European road mobility during the Marshall Plan years

Push" and "Pull" Factors in Technology Transfer Moving American-Style Highway Engineering to Europe

The Agricultural Revolution of the 20th Century

The 'COVID war '? Reflections on mechanisms and imprints of the COVID-19 pandemic

The Environmental Impacts of the UK Military Sector, Scientists for Global Responsibility -Declassified UK

How deep is incumbency? A 'configuring fields' approach to redistributing and reorienting power in socio-material change

Energy Myths and Realities: Bringing Social Science to the Energy Policy Debate

Grand Designs: historical patterns and future scenarios of energy technological change. historical case studies of energy technology innovation

Coal Or Oil as Fuel for the Navy

This work was supported by James Anderson and Baillie Gifford & Co.