When and how did the modern world become an international one? Jens Bartelson, a leading scholar of the history of international thought, provides new answers to this question by analyzing how relations between polities have been conceptualized across different historical contexts from the sixteenth century to the present day. A global intellectual history of the international system, this book challenges the widespread assumption that this system emerged as a result of a transition from empires to states, instead proposing that the international realm is but a continuation of imperial relations by other means. Showing how the international system spread through the creative appropriation of European concepts of nation and state by non-Europeans, Bartelson argues that this system has taken on a life of its own, to the point of becoming an empire in its own right.