The concept of power has long been a central yet contested part of the study of international relations. But power, like all other political concepts, has a history of its own. This book tells the story of how power among polities has been understood from the early modern era to the present day, arguing that conceptions of power in international politics have been characterized by significant continuities and swift ruptures during this period. It shows how notions of power have spread across cultures and evolved into an apple of discord that has drawn polities together into an international system premised on its uniformity and scarcity. Power Among Polities is the first intellectual history of power in international relations to date.