This work addresses how traditions associated with canon law of late medieval international society granted authority to myriad polities in fifteenth and sixteenth century questions of societal governance. In international relations, the late medieval period has rarely been given much attention; scholars have argued that the late medieval period is too “local” of an event to be considered within broader historical discussions of international societies and systems. This, however, is highly ironic considering that late medieval international society saw itself in universalist terms. It is precisely because late medieval international society was founded upon universalism, but organized on the basis of particular polities that it is such a valuable resource for understanding modern international society.

I provide a historical narrative of the process in which a “tradition of canonical status” developed and allowed multiple political actors to all claim authority based upon the same universal foundations; this “tradition of canonical status” is understood as the set of historical practices, norms and ideas—starting as early as the second and third centuries—that allowed the formal system of canon law to develop in the twelfth century. I argue that it did not disappear with the inception of a formal legal system, but rather its customary practices took place in the context of the new legal system. The narrative then explains how this tradition of canonical status was brought into the Reformations era—which is periodized here as 1414–1563—and in doing so it illustrates the traditional character of the period, which runs counter to both historians' and IR scholars' renditions of the era as a sharp break from the past.

In international relations, this sharp break is associated with the emergence of the modern nation-state and sovereign territoriality. This work instead argues that myriad polities continued to base their authority on the tradition of canonical status, which I demonstrate through a discussion of outcomes at societal congresses. Specifically, in the fifteenth century, the predominant theme was the debate regarding conciliarism—the school of thought that viewed the council as potentially the highest societal authority—while the sixteenth century, or the period of confessionalization, was dominated by discussions of documenting discordant understandings of previously shared practices. Out of these historical processes arose the “invention of religion”: before the sixteenth century, the religious and the political were inseparable, while after this religion and politics became distinct but interdependent. Their continuing interdependence informs an understanding of the gradual, but not inevitable process towards modern international society based on territoriality.