The conventional story of sovereignty told in the discipline of International Relations (IR) tells us that there is a “traditional” or “Westphalian” meaning of sovereignty that has prevailed since the seventeenth century and that accords states the right to govern themselves free from outside interference. In recent years, the tale goes, this meaning has been challenged for the first time by notions of conditional and responsible sovereignty. This article argues that the supposed “traditional” meaning of sovereignty is not as foundational and timeless as is often assumed. Rather than a right of non-intervention, it was the right to wage (just) war that was first conceived by political theorists to be the external corollary of the internal supremacy of the sovereign. This included the right of war to punish tyranny and rescue the oppressed. This article examines the initial absence and then the gradual emergence of the “traditional” meaning of sovereignty, arguing that it was only firmly established by international society for the first time in the twentieth century. It concludes by considering some of the implications of this revised story of sovereignty for the study of IR.