Recently, historians of the international system have called into question the significance of the Treaties of Westphalia in 1648 as the moment when the international system formed. One of their primary arguments is that the non-intervention norm typically associated with Westphalian notions of sovereignty developed much later. This paper will examine the early 17th-century debates over the right of the Pope to depose monarchs in the defense of spiritual matters. I read Part III and Part IV of Hobbes’ Leviathan in its intellectual context to see how his theory of sovereignty was partially developed to support a theory of non-intervention. This reading leads to two important contributions to current political science debates. First, it refutes the growing consensus that non-intervention developed as an aspect of sovereignty only in the late 18th and early 19th century. Second, the paper addresses current attempts to assert a right of humanitarian intervention. By exploring similarities between these recent debates and those between Bellarmine and Hobbes in the 17th century, I offer a fresh perspective on what is at stake in current claims to international community.