How does sovereignty order international politics? This question has inspired a rich body of literature unpacking the concept. Nevertheless, sovereignty remains taken for granted in large parts of the discipline of International Relations (IR) and, as a result, its role in ordering international politics is either ignored or misunderstood. This holds particularly true in areas of politics that are considered to challenge the foundations of the modern state system, such as international environmental politics or the politics of outer space exploration. How does sovereignty shape international efforts to combat climate change? Likewise, how does the conquest of extraterrestrial space impact the use of sovereignty on Earth? Starting from the premise that sovereignty is a complex, historically contingent and socially constructed concept, this thesis answers these questions by liberating the study of sovereignty from its traditional confines.

The first part of the thesis focuses on establishing sovereignty studies as a distinct subfield of IR and identifies its strengths and weaknesses. I argue that understanding the role of sovereignty in ordering international politics requires us to re-think deep-seated assumptions about sovereignty in IR literature, most importantly the association of sovereignty with equality. In order to do so, I highlight the neglected role of sovereignty in producing and maintaining hierarchies among states. This is articulated in a theoretical framework combining the logics of segmentation and stratification to explain the dual role of sovereignty in ordering international politics.

This theoretical framework is operationalised in the second part of the thesis, which focuses on international environmental politics and the politics of outer space. Individual chapters highlight the workings of sovereign segmentation and stratification in both domains. I challenge the unproductive repetition of debates on the resilience versus the obsolescence of sovereignty and outline an alternative way forward by showing how a sophisticated understanding of sovereignty can help us understand both change and continuity even in areas of politics that seem to stretch the modern state system to its limits.

Finally, the thesis argues that the insulation of sovereignty studies is symptomatic of a wider problem experienced by IR scholarship: its relative failure to export new insights outwards. In particular, I explore the relationship between IR and International Law and the ways in which the study of sovereignty within both disciplines illustrates the asymmetric nature of existing interdisciplinary dialogue. Taken together these three sections demonstrate the importance, for IR and other disciplines, of understanding the complex ways in which sovereignty both shapes, and is shaped by, the world we live in today.