This dissertation critically examines the political implications of the Westphalian system—a framework that has long dominated International Relations (IR) theory. Despite sustained historical critique, the Westphalian model remains the conceptual bedrock for understanding contemporary international society. By contrasting this system with the heteronomous social order of medieval Europe, this study illuminates fundamental divergences in political structure, subject formation, and the logic of exclusion. It argues that modern international society is constituted through the interrelation of sovereign states, existentially unified subjects, and a political order structured by friend-enemy distinctions. In contrast, medieval Europe was characterized by overlapping authorities, a limited monopolization of violence, and subjects shaped by internal contradiction. Far from producing mere disorder, this heteronomous arrangement mitigated radical exclusion and enabled a distinctive form of inclusion. Ultimately, this dissertation calls for a critical rethinking of the Westphalian paradigm, proposing heteronomous society as a viable conceptual alternative for International Relations.