This chapter explores competing American accounts of the Weimar Republic and their significance for IR during the interwar period. It focuses on two interpretations of the Weimar Republic in the context of German sovereignty and regime change. Hermann Mattern argued that the Weimar Constitution put an end to the legal debate about the location of sovereignty in the German polity. Rupert Emerson, on the other hand, regarded the revival of German Federalism as part of an international trend towards fragmented sovereignty and as a potentially positive step into the direction of a new, ‘post-sovereign’ international order. Both interpretations highlight the importance of the American experience of the state, of sovereignty and of the Civil War for shaping academic discourses on sovereignty, and the occurring rift between the ideal of legal sovereignty and its political reality prefigured realist theorising.