Which forms of political association promote peace? Peace is usually connected with cosmopolitan unity or the oneness of humanity. My exploration of the relative benefits of a society of states and the pluralistic orders it creates for peace challenges this view. In this dissertation, I examine Hannah Arendt's thoughts on political association. Extensive engagements with three different institutional models characterize Arendt's work: the nation-state (in The Origins of Totalitarianism), the ancient polis (in The Human Condition), and the modern republic (in On Revolution). My study traces the main features of these models and shows how Arendt's interest in and understanding of constitutional law and participatory politics lead her to reject both abstract legalism and all-too-concrete nationalism. In my view, Arendt's writings evince an acute awareness of how difficult it is to balance the domestic need for robust political participation, public spirit, and care for a particular political "world" with the need, at the inter-state level, to create and maintain a framework of international law. I argue that Arendt's political theory does not founder on this tension. Arendt underlines the need to maintain a tense equilibrium between these two poles, which is required if we are to avoid the cosmopolitan privileging of international law and institutions above all else. Similarly, such a tense and consciously maintained equilibrium enables us to avoid the nationalist conclusion that, in order to be self-governing, a state must possess more or less unfettered sovereignty. In order to back up these assertions, I investigate Arendt's novel idea of federalism and her notion of how a constitutional regime can be "augmented and preserved." Arendt's concepts of constitutional augmentation and federalism allow us to bridge the gap between domestic and international politics. Indeed, her thought suggests the possibility of re-conceiving of states in a way that does justice to both intra-state and inter-state relations. The potential result is something neither idealistic cosmopolitan theory nor conventional realist theory can offer: a nuanced and well-articulated model of a pluralistic society of states.