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The Catholic Origins of Modern International Relations Theory

When teaching the history of the field of International Relations (IR), scholars tend to start with the classical author of The Peloponnesian War, Thucydides, then skip immediately to the early modern political theorists Machiavelli and Hobbes.  In the process, they ignore the entire medieval period and, therefore, the rich history of Catholic international thought that flourished in that period.  There are, of course, exceptions to this rule.  Reinhold Neibuhr, for example, famously drew on the works of Saint Augustine as he helped launch the school of international relations theory known as Realism in the mid-20th century.  But this is the exception.  For the most part, the great Catholic international thinkers of the Middle Ages are simply erased from history.  This is my humble effort to undo that grave error.

Augustine:  Human Nature and International Relations

Augustine of Hippo, admittedly a figure of late antiquity but crucially important to understanding medieval political thought, is typically introduced to students as the founder of Just War theory.  While this is certainly an apt description of the Doctor of Grace, it does not fully capture his contribution to the Realist tradition of international thought.  As Reinhold Niebuhr and other 20th century Realists have pointed out, Augustine’s primary contribution is his insight that politics are driven by the lust for power (libido dominandi) and that this results in international relations that inherently conflictual.  As Augustine put it: “The dispute between Cain and Abel proved that there is enmity between the two cities themselves, the City of God and the city of man. Accordingly, there are battles of wicked against wicked. There are also battles of wicked against good and good against wicked. In the 20th century, this became known as the “first image” explanation for war – the view that wars result from human nature and are, therefore, an enduring element of political life.  And this leads to his second insight, that the prospects for political progress, and especially for political perfection, are vanishingly small.  Humanity is fallen, and “insofar as men are sinful, the threat of war hangs over them, and hang over them it will until the return of Christ.”

John of Paris: Inventing the Idea of Sovereignty 

John of Paris, writing in the context of the turn-of-the-fourteenth-century dispute between King Philip IV of France and Pope Boniface VIII, invented the idea of sovereignty that was later (erroneously) credited to Jean Bodin.  John made two arguments about the constituent units of the medieval international order.  First, he articulated a radically new vision of what those units looked like – one that vested supreme temporal authority to legislate, command, and judge not in the universal Empire, but in territorially limited and autonomous kingdoms. According to this new model, supreme authority was vested neither in the pope nor the emperor, nor was it divided between coordinate temporal and spiritual powers (kings and popes). Instead, it was vested exclusively in the king, who held it directly from “the people,” without any papal or imperial mediation.  Second, John discussed the relationship between these sovereign states.  Specifically, he argued that such states were autonomous, independent of both each other and the Empire.  Although he didn’t discuss international relations directly, John is nevertheless important to the Realist traditions in that he theorized for the first time the nature of the sovereign states that comprised the international system of his day.

Aquinas: Conceiving States and the State System

The Angelic Doctor’s contribution to the tradition of Realist international thought was twofold.  First, he established definitively that the kingdom (what we would call the state) was the appropriate scale for the “perfect” or “complete” community.  Whereas Aristotle thought the city-state was the appropriate scale for such a community, and pro-imperial thinkers such as Dante and Englebert both thought universal empire best fit the bill, Aquinas maintained that the scale of polity best suited to human flourishing was the state.  Second, following Aristotle, Aquinas assumed that there existed – and ought to exist – a diversity of kingdoms.  For him, the appropriate form of government for each kingdom would be determined by factors such as language, way of life, law, habit, customs, and what each considered to be virtuous.  Taken together, these two insights implied an international system comprising independent states, each pursuing their own national interest, in a system lacking any universal government or superintending temporal authority.

Dante: Theorizing Anarchy as the Cause of War

Dante approached international relations slightly obliquely.  His primary purpose in both Convivio and Monarchia was to demonstrate the superiority of universal empire over a system of sovereign kingdoms.  In making the case that universal empire was the necessary scale for a complete or perfect political order, however, he made an important contribution to the study of international relations.  He argued that absent a global sovereign, human cupidity would naturally and necessarily generate quarrels among independent kingdoms.  For him, the “factory settings” for a pluralistic world order were discord, conflict, and war.  Indeed, Dante argued, the very point of a universal empire was to “ensure that kings be content to remain within the bounds of their kingdoms, and thereby to keep peace among them.”  For him, the natural disposition of an international system comprising sovereign kingdoms interacting under conditions of anarchy was not toward peace, justice, and concord. Instead, such a system was naturally and necessarily predisposed to war.

Dubois: Imagining Cooperation as the Solution to War

The royal publicist Pierre Dubois also came to view what we would now call the “anarchic international system” as an important, if largely permissive, cause of war.  Such an international system, he argued, by its very nature lacked a universal political power that could adjudicate disputes between kingdoms and other lesser powers and so maintain the peace.  As a result, Dubois argued, the conflicts that naturally arise between political units pursuing their own interests can only be resolved by arbitration, diplomacy or, if those two fail, war.  For Dubois, this argument took a very specific form: war was caused by the lack of an international council charged with maintaining the peace between sovereign principalities – what we would now call providing “collective security”


Why have even the most historically minded IR scholars ignored the contributions of medieval Catholic thinkers to the long tradition of Realist political thought? While it is probably impossible to answer this question conclusively, it seems reasonable to conjecture that Enlightenment prejudices regarding the medieval era and Reformation ones regarding the Catholic “dark ages” are at least partly to blame.  To proponents of both the Enlightenment and the Reformation, the medieval period was framed as a time of “darkness”  — for protestant reformers, the darkness of papalism, error, and corruption; for Enlightenment progressives, the darkness of clericalism and (religious) superstition – and contrasted (unfavorably) with the new age of religious or scientific progress.  The effect of this was not merely to portray the Middle Ages as a transitional period between classical (and biblical) antiquity on the one hand and either the Reformation or Enlightenment on the other, but to invest the period with precisely those qualities or characteristics most loathed and feared by both protestants and early modern humanists: religious superstition, papal and imperial hierarchy, ignorance, political decay, and economic stagnation.  Simply put, although they sought to advance different political agendas, both protestant and Enlightenment reformers were motivated to portray the medieval world as both radically different from and radically inferior to the worlds of revived classical or biblical antiquity they were seeking to create.  They simply could not believe that medieval thinkers could have anything serious to say about the emerging ‘science’ of international politics.

But if the precise reasons for embracing the nothing-important-happened-in-the-dark-ages perspective are difficult to discern, the detrimental impact that this embrace has had, and continues to have, on our understanding of international relations is not.  Beyond the undeniable fact that it has blinded us to a half-millennium of productive theorizing about the relations between states, the most significant negative consequence of the embrace of this perspective is that it has severed early modern political thought from its medieval headwaters, preventing us from understanding the historical roots of early modern innovations in the field of International Relations.  Thinkers like Machiavelli, Bodin, and Vattel did not invent modern international relations theory out of whole cloth. Instead, they assembled it out of the intellectual resources inherited from their medieval, and Catholic, forebears.  While the specific questions they sought to address may have been unique to the early modern moment, and while there is no gainsaying the novelty of their contributions, it is a central aim of this book to demonstrate that the early modern theorists of sovereignty were in a very real sense the apotheosis of a centuries-long medieval tradition of philosophical speculation about the locus, meaning and justification of supreme authority.  This is not, of course, to make the teleological and ultimately whiggish argument that the early modern concept of sovereignty was an inevitable consequence of medieval speculation.  Nor is it to assume that the work of Bodin, Vattel, and other early moderns was the culmination of some inexorable march of progress. But it is to argue that the early moderns were able to reason about international affairs in the way they did only because the conceptual raw materials they needed to do so were inherited from their medieval forebears.  And that is an important corrective to the hubris of those early moderns, protestant and humanist alike, who presumed to know better than their medieval and Catholic forebears.

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