Not So Innocent: Clerics, Monarchs, and the Ethnoreligious Cleansing of Western Europe

Ethnic cleansing, genocide, civilian victimization, and coercive demographic engineering have been widely examined as puzzles of international relations scholarship, including in recent case studies on Africa, the Americas, Asia, and Europe.¹ Ethnic cleansing has far-reaching consequences. It fundamentally reshapes the cultural, economic, and political features of a political unit, and it is often associated with modern nation-building. Why are ethnoreligious minorities eradicated through a mixture of expulsions, forced conversions, and massacres in some polities but not in others? This article develops a novel theoretical explanation by focusing on the campaigns of ethnoreligious cleansing against non-Christians that swept across numerous Western European polities corresponding to present-day England, France, Hungary, Italy, Portugal, and Spain from the eleventh to the sixteenth centuries.

Demographic engineering through ethnoreligious cleansing is a prominent feature of conflicts around the world. In the Middle East, Iran's demographic engineering in support of Bashar al-Assad's regime in Syria through ethnoreligious cleansing includes settling pro-Iranian Shiites from Afghanistan, Iraq, and Lebanon in strategic locations where Sunnis have been forcibly displaced or killed.² In Europe, Russia has been engaged in demographic engineering since it first intervened in Ukraine in 2014. Some international organizations and experts opine that Russia's war crimes constitute genocide.³ Ethnoreligious cleansing also occurs outside war zones. In South Asia, the military in Myanmar, supported by militant Buddhist monks, has been killing and systematically displacing Muslim Rohingya in what the United States recognizes as a genocide.⁴

Extant scholarship maintains that ethnic cleansing is a modern phenomenon. It is often explained by the rise of democracy or nationalism, or both. “Murderous cleansing is modern, because it is the dark side of democracy…. [It] has been moving across the world as it has modernized and democratized,” as Michael Mann succinctly summarizes.⁵ The assumption of ethnic cleansing's modernity is in part why many works on the topic explicitly focus on the twentieth century.⁶ Only some democratizing and modernizing states engage in large-scale ethnic cleansing, however, whereas many others do not. To explain this variation, scholars emphasize how wars and “the pre-war domestic or international conditions” enable or facilitate ethnic cleansing.⁷

Existing accounts of ethnic cleansing cannot sufficiently explain my outcome of interest: the eradication of those considered to be non-Christians by the Catholic Church across medieval Western Europe. First, ethnoreligious cleansing took place on a continental scale in medieval Western Europe, where the polities were neither democratic nor nation-states. Second, the extant scholarship does not adequately account for when supranational actors (e.g., clergy under papal leadership) played a key role in campaigns of ethnoreligious cleansing. These shortcomings are related to the empirical focus on modern case studies in which nationalist actors undertake ethnic cleansing to divide the world into nation-states. By contrast, my argument is in part compatible with works that emphasize domestic coalitions between core and noncore ethnic groups and these groups’ alliances with international actors.⁸

My argument seeks to remedy these shortcomings with a new empirical focus and a new theoretical explanation of ethnoreligious cleansing. I argue that a political leader in a competitive geopolitical region will commit ethnoreligious cleansing if a strong supranational actor will reward them for doing so and credibly punish them for not doing so. Counterintuitively, my argument suggests that minorities who were loyal to the monarch were eradicated (Jews and Muslims were “monarchical property” in medieval Europe) because of pressure from supranational papal-clerical actors. This pattern is almost exactly the opposite of the one that scholars identify in nationalist conflicts, whereby the minority group allied with an external actor competing against the local government is often eradicated. The fierce geopolitical competition for survival in medieval Western Europe was critical for this outcome because it forced local monarchs to comply with the papal-clerical demands to eradicate non-Christians. The monarchs and the papal-clerical actors were not in a conflict because of non-Christians primarily, but most Jews and all Muslims were eradicated during this conflict. A monarch who harbored and protected non-Christians despite papal-clerical reprimands risked being deposed, killed, and replaced with another monarch. Papal-clerical actors’ interventions across Europe were indicative of a “supranationalism that kills.”⁹

My argument on ethnoreligious cleansing is also relevant to the origins of nationalism. While the existing accounts present nationalism as the precursor of ethnic cleansing, my argument reverses that causality and chronology. I suggest that medieval ethnoreligious cleansing in Western Europe was the result of a supranational religious (Gregorian) reform that led to the rise of the clerical class and doctrinal change dehumanizing Jews and Muslims. Religious homogeneity forged by supranational actors ironically facilitated Western European polities’ transition to become the earliest nation-states. Moreover, this religious demographic legacy explains in great part the mono-religious (Christian-only) if not sectarian (Catholic-only) form that many Western European nationalisms assumed since their origins.¹⁰ Eradicating non-Christian communities was a critical step in transforming European polities from dynastically defined entities to demographically defined entities distinguished by their religious homogeneity. This transformation prefigures “nations.”¹¹

What enabled and motivated the clergy under papal leadership to push for the mass eradication of non-Christians starting in the eleventh century? The Gregorian Reform movement dramatically increased the powers of the papacy and the clergy, which are the main actors responsible for eradicating non-Christians. During this period, the Church also shifted its doctrine toward Jews and Muslims in a more exclusionary direction. This shift culminated in their dehumanization, which motivated the papal-clerical actors to push for them to be eradicated. The dehumanization of Jews and Muslims was in line with both the factional interests of the papal-clerical actors and their religious insecurity. First, Jews and Muslims were assets of the monarchs, defined as “serfs of the royal chamber” (servi regie camerae), making them monarchical property and targets of the papal-clerical actors in their struggles against the monarchs.¹² Second, Jews and Muslims were seen as religiously threatening, both because they were not converting to Christianity (even after decades under Christian rule), and because the clerics feared that contact with Jews and Muslims could lead to Christians’ conversion to Judaism and Islam. Papal-clerical pressure on monarchs to eradicate non-Christians ultimately succeeded because of a third factor: the geopolitical division of Western Europe into dozens of relatively small polities that were locked in a fierce competition for survival. A monarch who did not comply with the papal-clerical demands to eradicate non-Christians could be eliminated and replaced with another monarch who would comply with the papal demands.

The article proceeds as follows. The first section briefly reviews the extant scholarship on ethnic cleansing, genocide, classification of identities, and the origins of nationalism to identify their predictions, utility, and shortcomings in explaining my empirical puzzle. In the second section, I present my argument on ethnoreligious cleansing. The second section also includes detailed discussions of the three factors that facilitated the eradication of non-Christians. The third section specifies my empirical puzzle and case selection. The fourth section assesses the temporal and geographic variation in the eradication of Jews and Muslims across medieval Western Europe and evaluates some seemingly challenging cases that also confirm the predictions of my argument. The fifth section is comprised of case studies where non-Christians were eradicated. The sixth section discusses the contrast with non-Western polities, where much higher levels of religious diversity persisted. The conclusion discusses the theoretical significance, present-day relevance, and implications of my argument and findings.

Ethnic cleansing and genocide,¹³ as well as demographic engineering¹⁴ through ethnic exclusion¹⁵ and ethnoreligious population transfers,¹⁶ are outcomes that scholars attribute to the rise of the nation-state and democracy. Since the publication of Benedict Anderson's Imagined Communities and Ernest Gellner's Nations and Nationalism in 1983,¹⁷ if not earlier, nationalism has been depicted as a modern phenomenon.¹⁸ These accounts are insufficient in explaining ethnoreligious cleansing in medieval Europe. Relatedly, existing studies of ethnic cleansing usually focus on national- or subnational-level violence committed by national and often nationalist actors.¹⁹ I argue that the supranational perpetrators—that is, clergy under papal leadership—better explain the continent-wide waves of ethnoreligious cleansing. Raphael Lemkin, who coined the term genocide, discusses the eradication of Occitan heretics (so-called Cathars in later historiography) and Muslim Moors as two of the earliest genocides.²⁰ But these cases have not been examined by scholars of international security investigating the origins of genocide.²¹

My argument contributes to three different types of explanations of ethnic cleansing: domestic coalitions, geopolitical considerations, and the rise of new actors in charge of classifying and codifying social identities. First, some scholars argue that if multiple ethnic groups are brought together under the same political or civil society organizations, these organizations may become barriers against ethnoreligious cleansing.²² Robust multiethnic alliances and organizations, in turn, may indicate that nonethnic cleavages are dominant in a society. As H. Zeynep Bulutgil argues, “Countries with deeper nonethnic cleavages and more internal competition within the dominant ethnic groups should be less likely to use ethnic cleansing.”²³ These accounts of ethnoreligious cleansing are partially compatible with one critical aspect of my explanation: non-Christians were almost always allied with the local monarchs in their struggles against the clergy. Consequently, non-Christians were often targeted in anti-monarchical movements. For non-Christians to be eradicated, their main Christian political ally, who was often the local monarch, had to be defeated or coerced.

Despite their usefulness and partial compatibility with my argument, the predictions that follow from existing accounts based on domestic coalitions are incorrect for my outcome of interest in two critical ways. First, a deep cleavage among the “three orders”—the clergy, the nobility, and the peasantry—existed in medieval Western Europe.²⁴ The cleavage between the clergy under papal leadership and the monarchs persisted for centuries. I argue that such a deep nonethnic cleavage should have made ethnic cleansing less likely and more variable across different Western European polities, if the domestic coalitions arguments were true. But all Muslims, Jews, and others deemed non-Christian by the Catholic Church across England, France, Portugal, and Spain were eradicated. Indeed, history reveals a stunning lack of variation—no medieval Muslim community surviving anywhere in Western Europe by the sixteenth century. Second, according to domestic coalition arguments, a supranational actor, typically a socialist party, acts as a barrier against the local government's perpetration of ethnic cleansing. But in medieval Europe, these roles were reversed: supranational clergy under papal leadership was the main advocate for persecuting non-Christians. Moreover, the local monarch was often the non-Christians’ ally.

A second literature emphasizes geopolitical alliances and military strategic considerations during interstate wars as the critical factors that explain ethnoreligious cleansing. Alexander Downes argues that mass civilian victimization occurs when a state tries to win a war while minimizing its own war casualties.²⁵ Harris Mylonas suggests that states target noncore groups with ethnic cleansing if these noncore groups are allied with a revisionist adversary of the host state.²⁶ My finding that the monarchs were compelled by papal-clerical pressures to eradicate non-Christians because they faced fierce geopolitical competition partly supports these geostrategic accounts of ethnic cleansing.

There are two ways that the predictions from the geostrategic literature are incorrect for my outcome of interest. First, Jews, Muslims, and heretics were not allied with an expansionist geopolitical enemy that posed an immediate threat to the polities where they lived. On the contrary, as serfs of the royal chamber, non-Christians were often loyal servants and valuable assets of the monarchs. In targeting and eradicating non-Christians, the papal-clerical actors were eliminating “categories” of people allied with the monarchs.²⁷ If anything, it was the clerics who could be depicted as “fifth columns” of the papal government—yet they were not the victims but the perpetrators of ethnoreligious cleansing. Second, many episodes of ethnoreligious cleansing cannot be explained as desperate attempts to win a war because they occurred during peacetime.²⁸

The third literature that I draw on traces and explains the rise of new professional cadres who sought to classify and codify social identities and make society more “legible”²⁹ for the purpose of governing and shaping it through techniques of “population politics” that included ethnic cleansing.³⁰ Such studies examine how census categories influence identity formation and patterns of mass persecution in different parts of the world, such as Rwanda,³¹ South Africa,³² and the Soviet Union.³³ Most of these works suggest that “population politics” originated in nineteenth-century Europe,³⁴ but I suggest that they can be traced to the thirteenth century. An exceptionally influential work of medieval history in this vein that is relevant to my empirical puzzle is Robert Ian Moore's The Formation of a Persecuting Society. He argues that the dramatic increase in the persecution of diverse groups classified as “deviants”—such as Jews, homosexuals, and lepers in medieval Europe—occurred mainly because of the rise of a new class of literati.³⁵

The accounts that attribute a causal significance to the rise of the literati are compatible with my first independent variable: the rise of the clergy under papal leadership. Members of the clergy were the main actors conceiving and overseeing waves of ethnoreligious cleansing to achieve a particular conception of a perfect society, “a social order coterminous with the Church.”³⁶ Yet scholars who emphasize the role of the literati in such violence do not explain why this violence against non-Christians took place specifically from the eleventh to the fifteenth centuries. Nor do these perspectives explain why and how the Catholic clerics were able to have a decisive influence in medieval Western Europe in the first place.

Although some scholars explain ethnic demography as an outcome,³⁷ political science does not have a theory on the origins of religious demography, which is often accepted as an exogenous independent variable.³⁸ I approach religious demography as an outcome and explain why Western Europe achieved an unprecedented level of religious homogeneity. My thesis is an example of a “second image reversed” argument—a supranational authority shaping domestic politics and molding the demography of Latin Christian polities.³⁹

Many aspects of medieval state-building sprang from the rivalry of monarchs and popes. For example, Bruce Bueno De Mesquita argues “that the development of important institutions of the modern sovereign state are partially an endogenous product of strategic maneuvering between the Catholic Church and European kings over political control within their domains.”⁴⁰ Yet scholars have not inquired whether the momentous demographic changes, including the eradication of Jews, Muslims, and other non-Christians, are related to the competition between monarchs and popes, as I do in this article. I argue that the religious homogenization of Western European polities was the result of papal-clerical actors’ pressure on monarchs to eradicate their Jewish, Muslim, and other non-Christian subjects.

To summarize, scholars attribute demographic engineering (including ethnoreligious cleansing) to modern nationalists, whereas I implicate the supranational Catholic clergy led by the papacy as being responsible for the earliest wave of ethnoreligious cleansing that indelibly shaped Western Europe from the eleventh to the early sixteenth centuries. Such cleansing was undertaken for religious rather than secular purposes by clerical actors who also sought to undermine their non-clerical opponents. Moreover, this cleansing started during the medieval era and not the modern or early modern era. Together, these three components of my argument revise the existing accounts of ethnic cleansing and genocide.

I argue that three factors explain the ethnoreligious cleansing of non-Christians by the Catholic Western European monarchies: (1) the rise in the powers of the clerical order under papal leadership starting in the late eleventh century and peaking in the thirteenth century;⁴¹ (2) the Church's doctrine toward non-Christians becoming more exclusionary, which culminated in their dehumanization during the same period; and (3) geopolitical competition without a regional hegemon among Catholic monarchies. Together, these causal factors brought about the eradication of all Muslims and almost all Jews in Western Europe. Responding to papal leadership, the powerful clergy demanded that Western European monarchs eradicate non-Christians. The fiercely competitive geopolitical context compelled these monarchs to comply.

First, the Gregorian Reforms in the late eleventh century led to the gradual rise in the power of the clergy under papal leadership. This power reached its peak in the thirteenth century, most spectacularly under Pope Innocent III (1198–1216).⁴² The reforms that empowered members of the clergy (the first order) by liberating them from the interference of the monarchs and the nobility (the second order) also increasingly centralized clerical power in the papal government. Thus, clerical power and papal power rose together.⁴³

Second, the Catholic Church shifted its conceptualization of Jews and Muslims in an exclusionary direction. The exclusionary reconceptualization of religious minorities reached a critical threshold in 1215, when the Church issued measures in the Fourth Lateran Council to sartorially stigmatize and residentially segregate non-Christians. These measures culminated in non-Christians’ eventual dehumanization, which facilitated their eradication.⁴⁴ Material interests and religious insecurity motivated the papal-clerical actors to demand that non-Christians be eradicated. First, Jews and Muslims were assets and allies of the monarchs because they were legally defined as serfs of the royal chamber, which made them targets of the papal-clerical actors. Second, Jews and Muslims were seen as religiously threatening. Their refusal to convert to Christianity even after decades under Christian rule undermined the clerical belief in Christianity's superiority. Furthermore, the clerics feared that contact with Jews and Muslims could bring about Christians’ conversion to Judaism and Islam.

Third, geopolitical competition without a hegemon in Western Europe⁴⁵ enabled popes to occasionally act as kingmakers, which they doctrinally claimed to be since the Dictatus Papae in 1075.⁴⁶ This papal kingmaking, though rare, still exceeded that of religious leaders in other religious traditions. The concatenation of these three factors was unique to Western Europe.

The increasingly powerful clerical order under papal leadership lobbied for religious homogenization and deployed many papal-clerical agents and instruments of power (e.g., Crusades, excommunication, interdict, deposition of monarchs, the use of regular and secular clergy against monarchs, the unleashing of mendicant orders, authorization of Inquisitions, and approval or annulment of dynastic marriages) to compel monarchs to eradicate their non-Christian subjects. Under papal-clerical pressure to eliminate non-Christians, Western European monarchs had four options: comply with the papal-clerical request and eradicate non-Christians (compliance); resist and thus risk being deposed and replaced by another Catholic monarch (resistance); or more intriguingly, initiate eradicating non-Christians to secure papal-clerical support against rivals as the most Christian/Catholic monarch (outbidding). A strong monarch could also successfully ignore papal-clerical requests to eradicate non-Christians. In non-Western religious-geopolitical configurations, monarchs overruling religious authorities was the norm. The first three scenarios, resulting in religious homogenization, are summarized in figure 1.⁴⁷

The first independent variable facilitating the eradication of non-Christians is the rise of the powers of the clerical order under papal leadership. The institutional and geographical (i.e., Papal States in central Italy, including Rome) separation of the Catholic Church from temporal-political authorities, which can be traced to the “Gelasian doctrine” of the “Two Swords,” allowed the clerical and nonclerical authorities to have autonomous bases of power.⁴⁸ Despite this autonomy, both clerical and nonclerical authorities interfered in the domains claimed by each other. By the twelfth century, what is known as the Gregorian or “hierocratic” view became dominant within the Church: the spiritual authority (sacerdotium) claimed hierarchical superiority to the temporal authority (regnum), with the papacy theoretically delegating the temporal rule to the monarchs.⁴⁹

The clergy formulated the conception of society as consisting of three orders, with the clergy as the first order. This conceptualization prevailed as “an image of the social order” for a thousand years.⁵⁰ The clerical order (ordo clericalis) was the first of the three medieval orders. It included “those who pray” (oratores), the priests (sacerdotes), whose “exclusive possession of the ‘sacred’—everything directly connected with divine service”—endowed them with “authority” (auctoritas), led by the papacy.⁵¹ The clerical order was comprised of all the “secular” and regular clergy, including both monastic and mendicant (e.g., Dominican, Franciscan) religious orders.⁵² The second order included “those who fight” (bellatores, pugnatores, or milites), such as the knights and the nobility led by the princes and the monarchs endowed with “power” (potestas).⁵³ The remainder of Christian society consisted of the third order/estate, comprised of those who work (laborant) or the farmers (agricultoribus).⁵⁴

Papal-clerical power was a variable that remarkably increased with the Gregorian Reforms. The papal power rose with the papal election decree of 1059, which asserted that the College of Cardinals alone can elect the pope.⁵⁵ Pope Alexander II (1061–1073) was the first pope elected by the College of Cardinals. Papal powers increased significantly under his successor, Pope Gregory VII (1073–1085), who implemented the eponymous Gregorian Reforms and promulgated the Dictatus Papae (1075), which asserted the pope's right to depose emperors.⁵⁶ The purpose of the Gregorian Reforms was to subordinate monarchical power to papal-clerical power.⁵⁷ The Gregorian Reforms liberated the clergy from the control of secular powers by prohibiting lay powers from both making appointments or investitures of bishops and selling clerical offices (simony).⁵⁸ The papacy's power reached its peak in the thirteenth century,⁵⁹ with “its high point roughly from the papacy of Innocent III (1198–1216) to that of Boniface VIII (1295–1303).”⁶⁰ In contrast, the papacy had less power in the fourteenth century than in the previous two centuries, evidenced by the Avignon Papacy (1309–1377) and the Western Schism (1378–1417).⁶¹ Even in this period of relative weakness, however, papal powers did not fall to their pre-1059 levels because the papacy did not renounce the new powers that it claimed after the Gregorian Reforms. Finally, the papacy regained some of its strength following its relocation to Rome after 1418 (table 1).

deploying new papal-clerical powers against monarchs and non-christians. In line with the first independent variable of my theory, the rise in papal-clerical powers, excommunication only became dominant in the twelfth century. Excommunication separated the condemned from the sacraments of the Church. In its better known and more consequential “judicialized” form, a pope could depose and replace a monarch.⁶² Indeed, popes sometimes used excommunication to punish monarchs who harbored Jews and refused to eradicate heretics, Jews, or Muslims. Consider two decisions from the Fourth Lateran Council in 1215. First, the Count of Toulouse was excommunicated for failing to act against heretics and was replaced by the leader of the Albigensian Crusade, Simon de Montfort.⁶³ Second, after excommunicating Holy Roman Emperor Otto IV in 1210, despite “repenting of his offences” and having the support of Sicilian Muslims in his claim to Sicily,⁶⁴ Pope Innocent III recognized Frederick II as the next emperor.⁶⁵ Popes before and after Pope Innocent III deposed both emperors and kings.⁶⁶ Pope Boniface VIII (1294–1303) deposed three kings of France before he was attacked to prevent him from deposing another French king.⁶⁷

The interdict was a more extensive punishment than excommunication. All the people living in a territory placed under interdict were deprived of religious services because of the sinful conduct of their secular leaders, who were often monarchs.⁶⁸ Interdicts were most frequently used during the thirteenth century, such that under Pope Innocent III, “at least fifty-seven local general interdicts were in force.”⁶⁹ For example, Pope Innocent III famously placed England under interdict in 1208 because King John refused to accept the papal nominee as the Archbishop of Canterbury.⁷⁰ Interdicts were also used to punish monarchs who protected non-Christians. Hungary was placed under interdict twice because the monarch insisted on employing Jews and Muslims in official positions despite a papal-clerical prohibition against doing so.⁷¹ Supporting or defending an individual or an action that the Church condemned was the most frequent cause of an interdict during the thirteenth century.⁷²

Another new papal instrument indicative of rising papal-clerical powers was the papal embargo, which was adopted in 1179.⁷³ Its main purpose was to punish and discipline Western Christians who traded with Muslims, Jews, schismatics, and anyone else the papal-clerical actors disapproved of. Popes typically used embargos to target economic and other nonmilitary bases of power.⁷⁴ These policies sometimes also harmed Christian groups that the papacy was suspicious of, such as the merchants.⁷⁵ The papal-clerical policies that targeted non-Christians were an integral part of an intra-Christian power struggle between papal-clerical actors and their Christian opponents.

The Crusade was an instrument developed by the first popes of the Gregorian Reforms⁷⁶ and used for the first time in the late eleventh century.⁷⁷ Crusades significantly contributed to eradicating non-Christians. Muslims or heretics were the direct targets of Crusades, whereas Jews were also killed along the way. For example, the first Holy Land Crusade in 1096 began with a massacre of Jews in the Rhineland.⁷⁸ Internal Crusades, such as the Albigensian Crusade⁷⁹ and the Italian Crusades,⁸⁰ were another punitive way that the papal-clerical actors directly contributed to religious homogenization. Monarchs who protected non-Christians were punished through internal Crusades, because eradicating non-Christians was a key element of an otherwise intra-Christian power struggle between papal-clerical actors and their opponents.

Plenary indulgence (i.e., the remission of sins) was the most common incentive that the papacy offered Crusaders. One could obtain an indulgence for as little as forty days of participation.⁸¹ The papacy could also offer the lands that were being targeted in an internal Crusade, such as when Innocent III offered the lands of the Count of Toulouse as an incentive to undertake a Crusade against him.⁸² Another new papal instrument was the Inquisition to root out heretics, including “crypto-Jews,” and “crypto-Muslims.”⁸³ This measure “took on its regular, formal and enduring institutional form” only with the Inquisition in Toulouse in the early thirteenth century.⁸⁴

Mendicant orders authorized by the papacy, most notably the Dominicans and the Franciscans, were another new and influential papal-clerical instrument to eradicate non-Christians.⁸⁵ “From the establishment of these first and most important mendicant orders in the Roman Church early in the thirteenth century, until the end of the medieval period and even beyond, Dominican and Franciscan friars directed and oversaw virtually all the anti-Jewish activities of the Christian clergy in the West,” Jeremy Cohen contends.⁸⁶ Dominicans were deployed across France, Iberia, and Italy to convert Jews and Muslims and to fight against heresy.⁸⁷ Sometimes the papacy aligned with members of the diocesan clergy (e.g., the bishops)⁸⁸ and the nobility⁸⁹ against their monarchs.⁹⁰ Popes used another new instrument, the military orders, such as the Templars and the Hospitallers, to fight Muslims in the early twelfth century.⁹¹

The papacy could also influence the geopolitical competition among monarchs by authorizing colonization and territorial expansion.⁹² From Africa to the Americas, the papacy functioned as a supranational authority to adjudicate the territorial claims of competing Catholic monarchs. For example, Pope Alexander VI adjudicated the rival claims of Portugal and Spain both by demarcating the Western Hemisphere between Portuguese and Spanish zones of colonization and by formalizing the Treaty of Tordesillas in 1494. Papal authorization for territorial expansion provides a key incentive for the mechanism of outbidding, whereby rival monarchs competed to present themselves as the most “Catholic monarch.” Outbidding in part motivated the final expulsions of Jews and Muslims from Iberia. Popes could also influence the geopolitical competition by annulling or authorizing dynastic marriages and political unions. For example, the papacy aided the union of Castile and León in 1230.⁹³ Similarly, King Ferdinand II of Aragon and Queen Isabella I of Castile could marry only with papal approval because they were related. Their marriage created Spain.

There were two separate developments that motivated papal-clerical actors to want to eradicate non-Christians in the first place. The first development was the redefinition of non-Christians as monarchical property. The second development was the clerical actors’ redefinition of non-Christians as no longer human. Both developments occurred after the Gregorian Reforms.

During the twelfth and the thirteenth centuries, influential papal-clerical actors such as the Cluniacs and the Dominicans dehumanized and demonized non-Christians.⁹⁴ Papal-clerical actors tried (but mostly failed) to convert Jews and Muslims in this period. This resistance to conversion led the Catholic Church to view Jews and Muslims as inhuman.⁹⁵ As Julia Costa Lopez demonstrates, “those who do not convert” were redefined as “no longer human” through a “process of Christianising reason.” This redefinition made their “elimination … a much more legitimate practice.”⁹⁶ Furthermore, they were depicted as “contagious” and threatening because they could convert Christians to Judaism and Islam.⁹⁷ In the words of Tomaz Mastnak, “The utopia of converting the Muslims turns out to be the dystopia of preventing Christians from falling into heresy.”⁹⁸ The fear of contagion motivated papal-clerical actors to enact new policies to minimize Jews’ and Muslims’ contact with Christians. For example, the Fourth Lateran Council of 1215 mandated that Jews and Muslims be segregated into ghettos and stigmatized (forced to wear a badge).

In the struggle between the monarchs and the papal-clerical actors, the clergy targeted non-Christians because their codification as serfs of the royal chamber identified Jews and Muslims as monarchical assets.⁹⁹ This codification was a significant change to the previous status of non-Christians: “The onetime free Roman citizens became ‘our Jews’ (Iudei nostri), the possessions of the castellans, counts, or kings on whose land they lived, like some sort of chattels.”¹⁰⁰ This formal codification occurred in 1236,¹⁰¹ but the conceptualization of Jews (and, by extension, Muslims) as serfs of the royal chamber can be traced back to the late eleventh century in parts of Aragon, Castile, England, and the Holy Roman Empire.¹⁰² I suggest that Jews and Muslims were harmed whenever the papal-clerical actors or the nobility prevailed in their struggles against the monarchs. Several key historical developments corroborate this line of reasoning. The Magna Carta (1215) in England¹⁰³ included clauses that targeted Jews, and both the Golden Bull (1222) and the Oath of Bereg (1233) in Hungary¹⁰⁴ included clauses that targeted Jews and Muslims. Thus, these documents represent victories of the papal-clerical actors, allied with the nobility in these specific cases, against the monarchical actors and non-Christians, who were targeted as monarchical assets. Similarly, “Jews in France were attacked as a proxy for the king himself.”¹⁰⁵

The people who were not members of the Catholic Church (extra ecclesiam) were increasingly subjected to similar laws and policies by the papal-clerical actors.¹⁰⁶ The new compilation of canon law, Liber extra (a.k.a. Decretals of Gregory IX), was completed by Raymond of Penafort in 1234 and included a specific section “On Jews, Saracens, and their Servants.”¹⁰⁷ Nineteen canons in this section targeted Jews, Muslims, or pagans, and many of them applied to all non-Christians.¹⁰⁸ Canon laws that previously applied to only Jews were extended to Muslims.¹⁰⁹ This extension indicated a “conceptual shift toward a binary classification of humanity” between Christians and non-Christians that culminated in Pope Boniface VIII's famous bull, Unam sanctam, which declared: “There is no salvation outside the Church of Rome.”¹¹⁰ It is in this period that some Christian authors even refer to the “Synagogue of … Muhammad,” demonstrating the extent to which they perceive non-Christian groups as one and the same.¹¹¹

Redefined as inhuman by the clergy and also as monarchical property separately, non-Christians were probably the largest social group that remained relatively illegible when, at the Fourth Lateran Council in 1215, the papal-clerical actors required that Catholic Christians take annual communion and sacraments. In the words of Robert Ian Moore, this requirement thus defined “the essential conditions of membership for all Western Europeans for the next three centuries.”¹¹² At the same meeting, papal-clerical actors also required sartorial stigmatization and residential segregation of Jews and Muslims by forcing them to wear badges and to reside in designated areas, or ghettos.¹¹³ The critical point for my argument is that the first mass expulsion of Muslims (from Sicily in the 1220s) and the first expulsions of Jews (from Anjou and Maine in France and from England in 1288–1290) occurred after the Fourth Lateran Council.

The third independent variable that facilitated the eradication of non-Christians was the fierce geopolitical competition among polities without a hegemon in Western Europe, which allowed the papal-clerical actors to successfully coerce or remove monarchs who opposed the ethnoreligious cleansing of non-Christians. Having powerful allies among the majority group might have obstructed the ethnoreligious cleansing of the minority groups.¹¹⁴ In seeking to eradicate non-Christians, the papal-clerical actors still faced a major constraint: the monarchs who claimed non-Christians as their property sometimes resisted papal-clerical pressures for ethnoreligious cleansing because they benefitted from these minorities, for example, by borrowing money from Jews and using Muslims as mercenaries.

Unlike non-Catholic monarchs in other regions, Catholic monarchs in Western Europe faced a unique dilemma vis-à-vis the clergy under papal leadership. Catholic clergy developed a united, hierarchical, and supranational organizational structure (led by the papacy) that held the balance of power among relatively small Western European polities that were in a fierce geopolitical competition (figure 2). The situation was almost exactly the opposite in regions dominated by non-Catholic religious traditions, as I discuss in the penultimate section of this article.

The Fourth Lateran Council accepted “the doctrine that a lord who failed to root out heresy could be replaced by a good Catholic who was willing to do what the Church required,”¹¹⁵ formulating what I call “the Innocent III doctrine.” If the definition of a “good Catholic” and a “heretic” depended on papal opinion, then it becomes clear that the papacy claimed expansive powers by 1215. This allowed “the pontifical imperialism inaugurated by Innocent III and sustained by his successors [that] sparked resistance in its turn from temporal rulers anxious to guard their privileges against an overreaching Church.”¹¹⁶ The geopolitical division of Western Europe allowed the increasingly powerful clergy under papal leadership after the Gregorian Reforms to coerce or depose monarchs who allied with and protected non-Christians, thereby removing the last major obstacle to ethnoreligious cleansing.

My dependent variable is the eradication of all Muslim communities and almost all Jewish communities across Western Europe, and the persecution of other significant categories of people considered non-Christian by the Catholic clergy led by the papacy.¹¹⁷ From 1064 to 1526, the Catholic clergy used deportations, forced conversions, and massacres to eradicate non-Christians across Western Europe. These campaigns made Western Europe the most religiously homogeneous region in the world. My explanation of ethnoreligious cleansing is applicable to the universe of cases, meaning any medieval Western European polity ruled by Catholic dynasties.¹¹⁸

Temporally, I examine the period from the papal election decree of 1059 until 1529, when the anti-Catholic dissent within Western Christendom could no longer be contained as it was expressed in a “formal legal protest against [the Imperial Diet of] Speyer earn[ing] them the appellation ‘Protestants.’”¹¹⁹ It is in this 470-year period that members of the supranational clergy, leveraging the powers of papal government vis-à-vis the monarchs, were able to facilitate eradicating all Muslims and almost all Jews across Western Europe.¹²⁰ After 1529, the Catholic Church failed to eradicate Protestantism, and anticlerical nationalism and secularism also developed. Although the reasons for the papal-clerical actors’ failure after 1529 are beyond the scope of my argument, studies on the origins of nationalism and secular institutions convincingly argue that the printing press was in part responsible. In explaining the origins of nationalism, Anderson famously argues that “print capitalism” and the Protestant Reformation dethroned Latin and propelled the rise of vernacular languages and national consciousness.¹²¹ In explaining the origins of secular institutions, Bulutgil argues that “printing deprived the clergy of their comparative advantage in the control of ideas” and “printing had an asymmetric impact on religious and secular ideas by making it harder to monitor the content of the books in circulation and by generating incentives to publish material with secular or heretical content.”¹²²

Victimization of civilians, especially by their own governments, is a puzzle because it is today considered both “morally wrong” and “bad strategy,” even during wartime.¹²³ The state loses significant material resources, people, and revenue when large numbers of civilians are killed or deported. Yet the mass victimization of all non-Christian minorities became the norm across medieval Western Europe. Though democracies may have a path “from voting to violence,” whereby political parties exploit ethnoreligious rivalries and anti-minority popular opinion,¹²⁴ monarchies in medieval Europe did not have to follow popular opinion. That a monarchy would destroy an important portion of the country's population and revenue base is even more puzzling, since monarchs derived economic and military benefits from having Jews and Muslims as their property.

Before their eradication, Muslims were the largest non-Christian minority in medieval Hungary, Italy, Portugal, and Spain, and Jews were the largest non-Christian minority in England and France (table 2). At about the twelfth century, there were many Muslim communities across present-day Hungary,¹²⁵ Italy,¹²⁶ Portugal,¹²⁷ and Spain.¹²⁸ By the end of the thirteenth century, all Muslim communities in the Balearic Islands, Hungary, and Italy were eradicated. By 1526, Muslims had been expelled from Portugal and Spain as part of the ethnoreligious cleansing that had restarted in the late 1400s.¹²⁹ During the same period, Jews were expelled from England, France, Portugal, and Spain and forced to convert to Catholicism in Southern Italy. The “heretics” in Occitania, present-day southern France, were also eradicated. Thus, not a single Jewish or Muslim community survived in England, France, Portugal, or Spain by 1526. In contrast, polities that were ruled by non-Catholic dynasties (e.g., Muslim, Orthodox Christian) continued to harbor various sizable religious communities. By the sixteenth century, the religious diversity that existed in places like Baghdad, Delhi, Kazan, and Thessalonica was nowhere to be found in Lisbon, London, Paris, and Toledo. By the early 1500s, if not earlier, Western Europe emerged as the most religiously homogeneous region in the world (table 3).

My methodology is based on the understanding of “causal mechanisms, cross-case analyses, and case studies” together constituting the research “triad.”¹³⁰ The empirical scope of my argument includes all Muslim communities who had lived for more than a century in Latin Christendom by the thirteenth century (map 1; online appendix C). Thus, I include the entire universe of relevant cases in my analysis. I also explain all the mass eradications of Jews at the “national” level (England, France, Portugal, Spain), some of the earliest region-wide expulsions (map 2; online appendix D), and the campaign against the heretics of Occitania (a.k.a. “Cathars”) (map 2). In studying these questions, I consulted authoritative publications on each case and on the general topics that I discuss (see online appendix E, “Discussion of Sources”).

The temporal and geographic variations in the eradication of non-Christians over the 470 years (1059–1529) that I evaluate in my study strongly support my argument's predictions. In this section, I first demonstrate qualitatively how the temporal variation of the largest, “national-level” eradications of Jews, Muslims, and heretics of Occitania are fully congruent with the peaks of papal-clerical power in the thirteenth and late fifteenth centuries.¹³¹ Second, I use data published by other scholars to show quantitatively how the variation in local Jewish persecutions in these countries also confirms the predictions of my argument. These two analyses encompass the entirety of my Western European sample. Third, I explain how the earliest anti-Jewish pogroms in the Rhineland and the extraordinary lag of the Papal States in expelling its Jewish population are both strong confirmations of my argument.

The variation in the national-level eradications of Muslims, Jews, and the heretics of Occitania correlates with the variation in papal-clerical powers, as my argument predicts (table 4). Most importantly, almost all the eradications (expulsion, massacre, or forced conversion) of Jews, Muslims, and the heretics of Occitania at the national and regional levels occurred at the two peaks of papal power (i.e., 1198–1308 and 1418–1529), which is exactly what my argument would predict. There was only one kingdom-wide eradication beyond these two periods of high papal-clerical power. The exception was the second expulsion of Jews from France (in 1394). But there were some local eradications of non-Christians in periods of “moderate” papal-clerical power.

According to data compiled by Robert Warren Anderson, Noel Johnson, and Mark Koyama on all local-level Jewish expulsions starting in 1100,¹³² Jews were expelled from the five Western European countries in my study during the two peaks of papal-clerical power in the thirteenth and the fifteenth centuries (table 5).¹³³ All Jewish expulsions occurred in the first peak period of papal-clerical power in England, and more Jewish expulsions occurred in France in that same period than in any other single period, whereas all or almost all Jewish expulsions in Italy, Portugal, and Spain occurred in the second peak period of papal-clerical power. Most significantly, none of these countries experienced the highest number of Jewish expulsions in either of the two periods when papal-clerical power was relatively low. Finally, the first region-wide (in Anjou and in Maine, 1288–1289) and nationwide (England, 1290) expulsions of Jews, and the first forced conversion of Jews across an entire region (Southern Italy, 1290–1293), all occurred in the thirteenth century, which is exactly what my argument would predict. France is the only partially atypical case for Jewish expulsions. Many Jewish expulsions occurred during the unusual Avignon Papacy, when seven consecutive French popes resided in Avignon (1309–1377) rather than in Rome.¹³⁴ In contrast, the Avignon Papacy resulted in decreased persecution of non-Christians beyond France.

Anti-Jewish pogroms in the Rhineland in 1096 and the extraordinary lag of the Papal States in expelling its Jewish population both provide strong confirmations of my argument. The Rhineland pogroms were directly related to the influence of papal power because these massacres were committed by the first Crusaders who were mobilized for holy war by Pope Urban II.¹³⁵ Holy Land Crusaders often massacred Jews and Muslims in Europe on their way to the Middle East.

Jews were not expelled from the Papal States throughout the 470-year period that I study. This might seem a strange anomaly, but I argue that the Papal States tolerated Jews because the popes themselves were also the monarchs in the Papal States. Thus, Jews were in the unique situation of being monarchical assets elsewhere in Europe and papal assets in the Papal States. My explanation of papal-clerical actors targeting Jews and other non-Christians is based on the separation and the struggle between papal-clerical and monarchial powers. This separation existed everywhere in Western Christendom except in the Papal States. Jews of the Papal States could therefore not be targeted by the papal-clerical actors as the assets of a rival monarch. Consequently, their survival in the Papal States throughout the five centuries that I examine provides an important and theoretically significant confirmation of my argument. In fact, some Jews who were expelled from Portugal, Spain, and elsewhere in Western Europe settled in the Papal States.¹³⁶

My explanation of ethnoreligious cleansing is probabilistic; some episodes of local eradications of non-Christians may not be adequately explained by the concatenation of the struggle between monarchical and papal-clerical actors, dehumanization of non-Christians, and geopolitical competition. Nonetheless, the evidence suggests that the temporal and geographic variations in all nationwide and region-wide eradications of Jews, Muslims, and the heretics of Occitania are congruent with my argument's predictions. Congruence, or correlation, does not mean causation. The next section uses process tracing and provides numerous causal process observations of the eradication of non-Christians, discussed in chronological order, in Sicily and Italy, France, England, Hungary, Portugal, Castile, Navarre, and Aragon.

The three independent variables of my theory—the rise of the clergy under papal leadership, the dehumanization of non-Christians, and the geopolitical competition among Catholic monarchs where the papacy tried to play the kingmaker role by supporting the monarchs who eliminated non-Christian minorities and punishing the monarchs who did not—facilitated the eradication of the entire Muslim population of Sicily and Italy and the forced conversion of Jews of Southern Italy. In many of the conflicts between papal-clerical and monarchical actors, the monarchical actor that the papacy targeted had the support of local Muslims. Thus, the monarchs defeated by the papacy were replaced by papally supported monarchs who eradicated Muslims. The papacy exploited the fierce geopolitical competition in Western Europe by rallying English and French monarchs against the Holy Roman Emperors who had been ruling Sicily and Southern Italy.

Muslim dynasties ruled Sicily for about 250 years.¹³⁷ By the late eleventh century, Muslims were the majority in Sicily.¹³⁸ At least until the 1120s, Muslims also constituted the majority in Malta.¹³⁹ A Christian dynasty, the Normans, completed their conquest of Sicily by 1091 and ruled until 1194.¹⁴⁰ For more than two centuries thereafter, Muslims lived under Catholic dynasties: the Hohenstaufens (1195–1266), and the Angevins (1266–1300).¹⁴¹

That the papacy of Innocent III was a negative turning point for the Sicilian Muslims supports my argument, given that historians consider his pontifi- cate as the zenith of papal power. Following the death of Queen Constance I of Sicily, imperial seneschal Markward von Annweiler took control of Western Sicily with the support of Muslims in 1199.¹⁴² Pope Innocent III used three different papal powers to defeat Markward and his Muslim allies: Markward and his supporters were excommunicated; all the places where they “arrived fell under interdict;”¹⁴³ and a Crusade was proclaimed against them. It was precisely Markward's alliance with the Muslims that Innocent III used to declare a Crusade against Markward, whom he described as “another Saladin” and “an infidel worse than the infidels.”¹⁴⁴ Finally, Markward and his Muslim allies were defeated by “the pope's coalition forces” at the battle of Monreale in July 1200,¹⁴⁵ which demonstrates how the papal-clerical forces successfully exploited Western Europe's geopolitical division to eliminate a Christian leader allied with non-Christians. In another conflict that pitted the papal-clerical actors against Muslims, Innocent III excommunicated the Holy Roman emperor, Otto IV, in 1210, while Sicilian Muslims supported Otto IV “as he attempted to extend imperial power on the island.”¹⁴⁶ French forces also defeated the excommunicated emperor at Bouvines in 1214.

Starting in the 1220s, Holy Roman Emperor Frederick II deported all Sicilian and Maltese Muslims to Lucera, a town on the Italian peninsula.¹⁴⁷ The papacy repeatedly urged the emperor to convert the Muslims of Lucera. Deploying a new instrument of papal power, mendicant orders, Pope Gregory IX (1227–1241) “wrote to Frederick to request that Dominican friars be allowed to visit Lucera [in 1233] to preach among its inhabitants.”¹⁴⁸ He raised the issue of conversion again in 1236.¹⁴⁹

The papal-clerical actors reprimanded Frederick II for his amicable relations with Muslims. From “portraying him as being more sympathetic to Islam than to Christianity” to accusing him “of committing sexual sins involving Muslims,” Frederick II's “association with Muslims figured regularly in the polemic writings of papal supporters.”¹⁵⁰ Gregory IX excommunicated Frederick II in 1239 and deposed him in 1245 at the First Council of Lyons, where “Frederick's support for Muslims in general and for the Muslim colony in particular was raised as a part of a larger effort to portray him as a heretic.”¹⁵¹

Papal forces invaded Southern Italy after Frederick II died. This invasion pitted the papacy against Frederick's son, Manfred, who “took refuge in the town [Muslim Lucera] in 1254, when fleeing papal forces.”¹⁵² Pope Alexander IV (1254–1261) issued a Crusader bull in 1255, condemning Manfred's coalition with the Muslims.¹⁵³ Exploiting the geopolitical competition in Western Europe once again by inciting England against the Holy Roman Empire, “the pope offered the crown of Sicily to Edmund, the young son of the English king, Henry III”¹⁵⁴ in order to convince him to fight Manfred. The “existence of a Muslim community in southern Italy provided a central justification for the launching of a crusade against Manfred in 1258.”¹⁵⁵ Thus, the pope attempted to depose and replace a monarch whom he denounced as an ally of Muslims. The next pope, “Urban IV, sought the support of Charles I of Anjou … against Manfred and the Muslims, with indulgences offered to those who would fight against them as if the campaign were a crusade.”¹⁵⁶ His successor, Clement IV (1265–1268), also declared a Crusade against the Muslims of Lucera.¹⁵⁷ The papal coalition succeeded, and at “the pivotal battle of Benevento in February 1266, Charles defeated Manfred and his Muslim forces.”¹⁵⁸ This defeat ushered in Angevin rule over Southern Italy.

After 1266, then, the papal-Angevin alliance was particularly instrumental in eradicating non-Christians.¹⁵⁹ When Conradin, the son of Manfred's half brother, rebelled to claim the crown, the Muslims of Lucera joined the fight against the Angevins. This alliance “served as the pretext for crusader preaching against them.”¹⁶⁰ Muslims lost again when Conradin was defeated in 1268. Having been handpicked by the pope, the Angevin king, Charles II, dismantled the Muslim colony of Lucera in 1300. Muslims were either deported to slave markets across Italy or killed for resisting enslavement.¹⁶¹ “Through all of this, the descendants of the Sicilian Muslims showed their characteristic if futile loyalty to the [previous] ruling dynasty [the Hohenstaufen], providing crossbowmen to both Manfred and Conradin.”¹⁶²

It is telling that when Charles II expelled the Jews of Apulia, they “initially took refuge in Lucera.”¹⁶³ The dynasty most closely allied with the papacy, the Angevins, destroyed Muslim Lucera shortly after it expelled Jews from Anjou and Maine in 1288–1289 and forcibly converted Southern Italian Jews in 1290–1293 (map 2). The Dominicans carried out this forcible conversion.¹⁶⁴ Jews as royal serfs were assets for the crown, and yet “the royal policy of toleration could not prevail against the Dominicans”¹⁶⁵ who were deployed by the papacy.¹⁶⁶ One famous Dominican, Ramon Llull, was deployed to convert Lucerine Muslims after having converted Jews and Muslims in Spain.¹⁶⁷ Under the threat of forced conversion, Jews fled to the Muslim colony of Lucera.¹⁶⁸ Different religious minorities seeking refuge in each other's safe havens is a recurring pattern across centuries, including during the Holocaust.¹⁶⁹

The summary of conflicts that involved Muslims and Jews in thirteenth-century Italy demonstrates that papal-clerical actors were consistently opposed to non-Christians, whose most common Christian allies were the monarchs. Papal-clerical actors deployed numerous instruments to successfully defeat multiple monarchs allied with non-Christians. They also exploited geopolitical competition to mobilize other monarchs to invade Italy to defeat adversaries of the papacy.

The eradication of so-called heretics who did not accept papal-clerical authority in Occitania was mostly achieved at the height of papal-clerical power in the thirteenth century. In this period, the papacy successfully exploited the geopolitical competition by rallying northern French and other actors to eliminate the counts, viscounts, and kings accused of not surrendering the heretics to the papal-clerical authorities. Their removals resulted in the French conquest of Occitania and the creation of France in roughly its current borders. Known as “good men” (bons omes) and “good women” (bonas femnas)¹⁷⁰ and labeled as Cathars in later historiography, these people did not accept the Catholic Church's religious authority. Historians debate whether they constituted a self-conscious religious community.¹⁷¹ What matters for my argument is that the papacy identified them as one of its most significant religious challenges and violently eradicated them.¹⁷²

Pope Innocent III “exhorted the King of France, Philip Augustus, or his son Prince Louis to act against heretics,” and he offered an indulgence “to those who would follow Philip south to exterminate heresy.”¹⁷³ He also warned the Count of Toulouse, “urging action against heresy and threatening the count if he did nothing.”¹⁷⁴ A papal legate was assassinated in January 1208 after excommunicating Raymond VI, the Count of Toulouse, “for refusing to publicly suppress heresy.”¹⁷⁵ This murder triggered the Albigensian Crusade, which Lemkin considers genocidal.¹⁷⁶ This campaign persisted for two decades and was a “savage internal crusade … that bordered on a war of extermination.”¹⁷⁷ The Crusaders’ most violent attacks targeted the territories of Viscount Raimon-Roger Trencavel and Count Raimon-Roger of Foix, both of whom had King Pere II of Aragon as their overlord.¹⁷⁸ For the second time and with prompt approval by the pope, clerical actors (including archbishops and bishops) excommunicated Raymond VI for refusing to hand over heretics.¹⁷⁹ Consequently, he was “dispossessed of his territories.”¹⁸⁰ Toulouse was placed under interdict in 1213.¹⁸¹ Even King Pere II of Aragon was killed by the Crusaders in 1213 when he came to aid Raymond VI and Raimon-Roger. Moreover, the leader of the Crusaders, Simon de Montfort, was recognized as the Count of Toulouse by the pope, demonstrating the papal-clerical actors’ “kingmaker” powers.¹⁸²

When Raymond died in 1222, “he was denied the last sacraments and burial in consecrated ground.”¹⁸³ Clerical actors continued to pressure his son, Raymond VII of Toulouse, who was excommunicated in 1225.¹⁸⁴ He eventually accepted the papal demand to eradicate heresy in 1229.¹⁸⁵ According to Moore, “It was in Toulouse that the papal inquisition took on its regular, formal and enduring institutional form [in 1233].”¹⁸⁶ The Inquisition consolidated the papal-clerical monopoly on religious authority by eliminating anyone who did not accept the Catholic Church's definition of what it meant to be a proper Christian.¹⁸⁷ Dominicans and Franciscans were deployed by the papacy to eradicate heretics of Occitania.¹⁸⁸ The Albigensian Crusade illustrates how the papal-clerical actors mobilized foreign fighters to punish local leaders who resisted the Church's effort to monopolize religious authority.

The first well-known allegation of a Jewish ritual murder of a Christian child occurred in 1144 in Norwich, England.¹⁸⁹ Gavin Langmuir identifies Thomas of Monmouth, a Catholic monk, as the main actor who invented and popularized this allegation in his hagiography of the child who became known as St. William of Norwich.¹⁹⁰ In addition to being the first Jews accused of ritual murder of Christian children, English Jews were also the first to be forced to wear the infamous badges starting in 1218, following the papal-clerical actors’ decision at the Fourth Lateran Council.¹⁹¹ According to Geraldine Heng, “In 1222, 1253, and 1275, English rulings elaborated on this badge for the Jewish minority—who had to wear it (men and women at first, then children over the age of seven)—its size, its color, and how it was to be displayed on the chest in an adequately prominent fashion.”¹⁹² In 1275, the “Statute of Jewry” required that Jews live only in the archa towns.¹⁹³ In a span of five years, Jews were expelled from England (1290) and from Anjou and Maine (1288–1289), and Southern Italian Jews were forced to convert to Christianity (1290–1293).¹⁹⁴

The papal-clerical actors’ redefinition of non-Christians’ status in the thirteenth century also facilitated eradicating Jews and Muslims in Hungary. In 1221, Pope Honorius III (1216–1227) reprimanded Hungarian monarchs for not releasing Christian servants and slaves of Muslims.¹⁹⁵ Leveraging such papal reprimands, and in accordance with the clerical-monarchical struggle at the heart of my argument, Catholic “prelates together with the emerging lower nobility, were involved in the movements against King Andras II's policies, which led to the promulgation of their privileges, the Golden Bull of 1222 and its rewriting in 1231.”¹⁹⁶ An article of the Golden Bull prohibited Jews and Muslims from holding public offices. In 1225, the pope referred to the decisions of the Fourth Lateran Council and “condemned the holding of public offices and of Christian slaves by Muslims and Jews” in Hungary.¹⁹⁷ Archbishop Robert of Esztergom “excommunicated several of the [Hungarian] king's advisers” and placed Hungary under an interdict in 1232 “because the articles of the Golden Bull … especially the articles concerning non-Christians, were not put into effect.”¹⁹⁸ The clergy, allied with the nobility, pushed for more autonomy and measures against non-Christians, culminating in the Oath of Bereg in 1233, which “consisted of two main sections, one concerning non-Christians, the other ecclesiastical privileges,” and “the king swore again not to employ Jews and Muslims.”¹⁹⁹ Hungary was placed under interdict again in 1234. Pope Urban IV admonished King Bela IV in 1263, and similar complaints by the bishop of Olomouc in 1272 and the Synod of Buda in 1279 forced “Kings Laszlo IV in the 1280s and Andras III in 1291 [to promise] not to employ non-Christians.”²⁰⁰ Persistent papal-clerical pressure succeeded and “Hungary's Muslims had disappeared by the fourteenth century.”²⁰¹

Following the temporal pattern predicted by my theory, Jews and Muslims across Iberian kingdoms were almost entirely eradicated during the two peaks of papal-clerical power. Papal-clerical actors explicitly and repeatedly urged Iberian monarchs to eradicate their non-Christian populations. For example, “[Pope] Clement IV warned Jaime of Aragon that the argument of usefulness could not warrant the retention of Saracens [Muslims] in his realm; they were to be expelled.”²⁰² Papal-clerical actors exploited the geopolitical competition both within Iberia and across Western Europe to punish monarchs who allied with or protected non-Christians. For example, King Pere II of Aragon was killed for siding with the protectors of alleged heretics during the Albigensian Crusade.

Iberian Muslims numbered “as high as 5.5 million” at the beginning of the twelfth century, but “probably between 500,000 and 600,000, out of a Spanish population of roughly 7 to 8 million” remained by the end of the fifteenth century.²⁰³ Iberia also had “the largest Jewish population in Europe.”²⁰⁴ The eradication of Muslims started with the Aquitanian, Burgundian, Catalan, and Norman armies’ capture of Barbastro and massacre of its Muslim inhabitants in 1064. This was arguably the first Crusade in history because it was supported by Pope Alexander II's letter granting indulgences to Catholics who fought.²⁰⁵ Causal process observations of how the papal-clerical actors used various instruments to eradicate Iberian Muslims include: the pope's granting of “Crusade-like status to the Catalan efforts to conquer Muslim Tarragona” in 1089;²⁰⁶ Aragonese capture of Tortosa in 1148 with the assistance of Templars;²⁰⁷ the role of Catholic orders including Hospitallers and Cistercians in colonizing Iberia with papal endorsement; Crusaders from England, Flanders, and Germany capturing Lisbon and massacring its Muslim population in 1147;²⁰⁸ and bishops and foreign Crusaders cooperating to capture the town of Alcácer do Sal in defiance of the Portuguese king's treaty with the Muslims.²⁰⁹

Castilian King Alfonso VIII, “fortified by a Crusade bull from Innocent III,” defeated Muslim armies in the battle of Las Navas de Tolosa in 1212. This victory “marked the beginning of a half-century in which virtually every Christian campaign in the peninsula up to the defeat of al-Azraq in the 1250s was formally qualified as a Crusade.”²¹⁰ Likewise, Aragon captured Mallorca in 1229 “with the aid of a papal Crusade bull.”²¹¹ In 1230, the papacy facilitated the union of two Iberian kingdoms, Castile and León, hence creating the most powerful polity in Iberia.²¹² In 1287, “a Crusade was duly authorized” for the Aragonese to conquer Menorca, which was followed by the enslavement of Menorcan Muslims.²¹³ By this time, most Iberian Muslims had already been expelled, killed, or forced to convert (map 1).

As previously noted, the Avignon Papacy and the Western Schism correspond to a period of papal weakness from 1309 to 1417. Papal-clerical power was revived and major Crusades to eradicate Muslims were relaunched in the late fifteenth century, with three Ottoman victories from 1448 to 1470 providing external stimuli for these Crusades.²¹⁴ A dynamic of “Crusader outbidding” became prominent, whereby competition to expand Christendom through conquest and colonization within and beyond Europe facilitated eradicating non-Christians (figure 1).

The final stage in eradicating non-Christians across Iberian polities (1492–1526) demonstrates how papal-clerical influence in an environment of geopolitical competition and religious outbidding could facilitate ethnoreligious cleansing. The papacy recognized Aragonese King Ferdinand II and Castilian Queen Isabella I as “the Catholic Monarchs” to reward them for defeating Muslims to conquer Granada and for expelling Jews in 1492. Although some Spanish Jewish expellees arrived in Portugal, the Spanish monarchs pressured Portuguese King Manuel I to expel the Jews in 1497 as a condition for marrying their daughter.²¹⁵

Historians attribute King Manuel I's decision to expel the Muslims in 1496 to his attempt to ingratiate himself with the papacy.²¹⁶ The Portuguese king likely “intended to bolster his reputation as a defender of the faith before the papacy as he struggled to obtain rights over the kingdom of Fez,” which the Spanish monarchs also claimed.²¹⁷ In his public letter to Pope Julius II (1503–1513), Manuel I claimed that “he was directly involved in persuading the Catholic monarchs of Spain … to put an end to the toleration of Islam in Castile in 1501.”²¹⁸ Manuel I's ostentatious efforts to appease the pope by claiming credit for eradicating Muslims in neighboring Castile and expelling Portuguese Muslims are striking examples of the religious outbidding that I identify in my argument. Castile followed Manuel's actions by banning the entry of Muslims in 1501 and then ordering all Muslims to convert or leave in 1502. Some Muslims chose mass conversion, such as “the entire [Muslim] community of Palencia.”²¹⁹ Navarre became the third Iberian kingdom to expel Muslims when it was “absorbed into” Castile and “became subject to its laws” in 1515.²²⁰ Finally, Emperor Charles V “obtained from [Pope] Clement VII (1523–1534) a dispensation absolving him of the obligation to honor the treaties and guarantees made to [his] Muslim subjects,” followed by their forced conversion in 1526.²²¹ Thus, the last Muslim community in Western Europe was eradicated.

The independent variables of my argument that facilitated ethnoreligious cleansing in Western Europe were missing in Islamic and Orthodox Christian polities. First, these polities lacked a single supranational religious leadership that acted as a kingmaker. Instead, multiple religious leaderships were subordinated to the monarchs. Second, there were Orthodox Christian and Islamic imperial polities that could be considered regional hegemons. Third, the Orthodox Christian and Islamic doctrines and the legal status of religious minorities did not facilitate their eradication. Given that all three of the necessary variables that explain ethnoreligious cleansing were missing, Orthodox Christian and Islamic polities were much more religiously diverse than Western Europe, as my argument would predict.

First, unlike the papacy in Catholic Christianity, both Orthodox Christianity and Islam had multiple religious authorities rather than one rigid hierarchy. Islamic caliphates (e.g., Baghdad and Cordoba caliphates) and Orthodox patriarchates (e.g., Antioch and Constantinople patriarchates) were located within the territories of a specific polity (e.g., Byzantine, Mamluk, Ottoman, or Russian). Importantly, their practical influence was often limited to the specific polity where they were located. Rather than a separation of powers as in Latin Christendom, Byzantine/Russian Orthodox polities were characterized by the notion of “Caesaropapism,” denoting subordination of the religious authority to the monarch.²²² In some Islamic polities, the same person was the monarch and the caliph (e.g., Ottomans). This dual role eliminated the struggle between the monarchical and the religious authority that facilitated ethnoreligious cleansing in Western Europe.

Second, there were significant differences in both the doctrinal and the legal status of religious minorities in Latin Christian and non-Western traditions. In the Orthodox Christian Byzantine Empire, the three-tiered legal system included: “common-law” regulating “the life of the Jews in their non-Jewish capacity” as citizens; “Jewry-law” regulating “the interaction of Jews with non-Jews”; and “the Jewish-law” that governed the remainder of Jewish life.²²³ Mark Cohen attributes the survival of Byzantine Jewry in part to “the tolerationist features inherited from pagan Roman legislation,” noting that the “Roman law had a continuous life in the late-antique Eastern Empire and its medieval Byzantine successor.”²²⁴ Furthermore, “the Latin Christian model of ‘Jewish serfdom,’ with its monarchical rights over the Jews and attendant arbitrariness, did not make significant inroads into the eastern Roman Empire.”²²⁵ Consequently, the second independent variable of my explanation of ethnoreligious cleansing was also missing in Orthodox Christian polities. Moreover, the Orthodox Church rejected key papal powers that were deployed in Latin Christendom to facilitate eradicating non-Christians, such as Crusades and indulgences. “The Byzantines had considered, but always rejected, the notion of Holy War,” and “the notion of the crusade disturbed the Byzantines.”²²⁶

The first Islamic polity established in Medina in the early seventh century included a legal framework to secure the religious autonomy of the city's Jewish community. This precedent continued as the Islamic empires expanded to include large Christian and Jewish populations. Under Islamic law, Christians and Jews paid the jizya tax in return for protection and communal-legal autonomy as dhimmi. “Under this system, each religious community had considerable autonomy to regulate its own internal affairs.”²²⁷ This autonomy “was granted to all religious communities, including Buddhists, Hindus, Zoroastrians, and Sabians, along with Jews and Christians,” although “the latter two were called the People of the Book to indicate the intimate connection of their religions with Islam.”²²⁸ For example, “at least a dozen legal traditions were practiced in the Ottoman Empire: five non-Islamic (Jewish, Armenian, Orthodox, Catholic, and Copt) along with four Sunni (Hanafi, Shafi'i, Maliki, and Hanbali) and several Shiite (such as Zaydiyya and Jafariyya).”²²⁹

Third, the regions of the world ruled by Orthodox Christian and Muslim dynasties had large imperial polities that could be considered regional hegemons (Byzantine, Mughal, Ottoman, and Russian Empires): “The Ming, Qing, Mughal, Ottoman, and Russian Empires were all an order of magnitude larger than France, Spain, or the Austrian dominions.”²³⁰ In contrast, the relatively small Latin Christian polities (Aragon, Castile, Navarre, Portugal) competed in Western Europe without a hegemon. Monarchs outside of Latin Christendom were far more secure vis-à-vis religious authorities because of their relatively higher power over them (figure 3; figure 4). Given the lack of a single supranational religious authority and the existence of hegemonic imperial polities, Orthodox patriarchs and Muslim caliphs could not act as kingmakers.

Given the absence of the three variables that I identify as leading to ethnoreligious cleansing, Orthodox Christian and Islamic polities historically had much more religiously diverse populations than Western European or Latin Christian polities. The higher religious diversity of medieval Islamic polities is established in extant scholarship and observable in the comparative treatment of Jews.²³¹ Ottoman cities such as Baghdad, Constantinople, Damascus, and Thessalonica boasted large Christian and Jewish populations.²³² In the 1520s, roughly 40 percent of the Ottoman population was Christian, and there were tens of thousands of Jews. By contrast, not one openly Jewish or Muslim community existed in England, France, Portugal, or Spain (table 2). Its religious diversity and legal pluralism led Karen Barkey to characterize the Ottoman polity as an “empire of difference.”²³³

Other Islamic polities (e.g., the Abbasids, Mamluks, Seljuks, and Umayyads) also boasted sizable Christian, Jewish, and other religious communities. Emperor Jahan-gir (1569–1627) of the Muslim Mughal dynasty in India is reputed to have said that “five sixth [sic] of the people of Hindustan [India] are idol-worshipping Hindus.”²³⁴ According to the first British census of India, its population was 73 percent Hindu and 21.5 percent Muslim. In addition, there were about three million Buddhists and Jains and more than a million Sikhs.²³⁵

The Orthodox Christian Byzantine Empire and the Russian Empire each had sizable non-Orthodox and non-Christian populations. “Armenians, Catholic and Greek Orthodox Christians, Jews (both Rabbinate and Karaite), and in some parts of the empire also Muslims (e.g., Sicily and Anatolia) occupied the same social space in the Byzantine domains,” Mark Cohen maintains.²³⁶ Estimates of the Jewish minority vary between 0.3–0.5 percent²³⁷ and 2 percent of the Byzantine population, or “close to 100,000” people.²³⁸ There was also a Muslim minority, most notably in Constantinople, for many centuries until the Ottoman Empire absorbed Byzantium.²³⁹ Armenians were the largest non-Orthodox Christian population who survived throughout the existence of the Byzantine Empire.²⁴⁰ Benjamin Kedar concludes that a “general expulsion from the Byzantine Empire appears never to have occurred.”²⁴¹ He argues that “corporate expulsion … constitutes a characteristic of Western European civilization.”²⁴²

The Russian Empire had significant Buddhist, Catholic, Jewish, and Muslim minorities.²⁴³ It was multireligious already in the sixteenth century, when “Muslim Tatars … represented at both elite and common levels … were treated in a manner similar to that of their Orthodox brethren.”²⁴⁴ The Russian Empire became more multireligious in its legal and political structure in the following centuries.²⁴⁵ In 1552, sizable Muslim populations came under Russian rule with the conquest of Kazan Khanate, which had a population of 400,000.²⁴⁶ Muslim Tatar nobility were accepted into the Russian nobility without having to convert.²⁴⁷ By 1719, if not much earlier, the Russian Empire also had sizable Buddhist populations.²⁴⁸ In sum, both Orthodox Christian and Islamic polities had much more religiously diverse populations than medieval Catholic Western European polities.

The significance of the ethnoreligious cleansing of medieval Western Europe in the making of the modern world can hardly be overstated. International relations scholars have studied how the “second order” and the “third order/estate” contributed to absolutist states and popular revolutionary movements, respectively. But I argue that the “first order” (oratores, priests) preceded the second and third orders in their formative causal role as the actors who created religiously homogenous polities across Western Europe. It was this religiously homogenous societal platform that leaders later used to build states and nations. My novel explanation of ethnoreligious cleansing in medieval Western Europe has theoretical significance, contemporary relevance, and implications for future research.

My argument has theoretical implications for the origins of ethnoreligious cleansing, genocide, and nationalism. Most studies of ethnoreligious violence in Europe focus on communal, regional, and national political dynamics to explain its outbreak and variation.²⁴⁹ I have attempted to describe and explain an alternative path to ethnoreligious cleansing that persisted for almost five centuries and that resulted in the eradication of all Muslim and Jewish communities living under Catholic rule in Western Europe by the early 1500s. Relatedly, the extant scholarship maintains that ethnoreligious cleansing is a modern phenomenon that is often committed by nationalist actors for secular purposes. My argument revises the conventional wisdom by unearthing and explaining the religious motivations, supranational actors, and medieval origins of ethnoreligious cleansing across Western Europe.

I have argued that the concatenation of three factors explains ethnoreligious cleansing of non-Christians in medieval Western Europe: (1) the papacy as a supranational religious authority with increasing powers after the Gregorian Reforms, (2) the dehumanization of non-Christians by the papal-clerical actors and their classification as monarchical property, and (3) the fierce geopolitical competition among Western European monarchs that made them particularly vulnerable to papal-clerical demands to eradicate non-Christians. I argue that political leaders commit ethnoreligious cleansing if they perceive it as necessary to survive against domestic or international rivals. The monarchs who refused to eradicate non-Christians faced serious threats by the papal-clerical actors and their allies. Not only did monarchs face interdiction, but they could lose their territories, their thrones, and even their lives in Crusades. The conflict between papal-clerical actors and the monarchs was not primarily over non-Christians, but all Muslims and most Jews were eradicated as part of this conflict.

Recent scholarship examines how the Catholic Church in medieval Europe contributed to the long-term political development and the “rise of the West.”²⁵⁰ But as I have demonstrated in this article, the actors that the literature credits with providing the foundation of modern state power and urban self-government in medieval Europe—the Catholic Church,²⁵¹ the Cluniacs,²⁵² the Crusaders,²⁵³ and the papacy,²⁵⁴—were also responsible for eradicating non-Christian minorities. I have previously argued that “the exclusion of Jews and Muslims, the two major non-Christian religious groups in Europe and the Americas, has continued on the basis of ethnic, racial, ideological, and quasi-rational justifications, instead of or in addition to religious justifications, since the Reformation.”²⁵⁵ In this study, I have sought to explain the medieval origins of Jewish and Muslim exclusion that took hold across all Western European polities in the five centuries preceding the Reformation.

My novel explanation of ethnoreligious cleansing also contributes to understanding recent and ongoing ethnic cleansing undertaken by actors leveraging the ideational and material support and even direct intervention of supranational hierocratic authorities. George Breslauer describes the Communist Party of the Soviet Union (CPSU) and the Roman Catholic Church as “hierocratic … institutions in which a ‘priestly corps’ of officials, staffing a centralized hierarchy, is charged with safeguarding the sacred values and proselytizing them among the laity.”²⁵⁶ The Soviet Union committed one of the largest waves of ethnic cleansing of the twentieth century.²⁵⁷ Both the CPSU and the Chinese Communist Party supported communist regimes undertaking both class-based and ethnic cleansing and mass killings around the world (e.g., the Pol Pot regime in Cambodia), which scholars call “communist genocides.”²⁵⁸ In these episodes of mass killings, local communist cadres leveraged the ideological and material support of the Soviet or Chinese Communist Party in massacring their non-communist countrymen. Such actions resemble the Catholic clergy's attack against non-Christians and their Christian allies in medieval Europe.

Some non-Christian supranational religious sectarian actors also abet ethnoreligious cleansing. With support from Iran and its supranational Shiite religious leadership, the “Assad regime [in Syria] is trying to ensure a Sunni-majority population cannot be recreated”²⁵⁹ by using a mixture of ethnoreligious massacres and expulsions. Local Shiite actors leverage supranational Shiite clerical/ideological influence, foreign fighters, and material assistance in violent conflicts in Iraq, Lebanon, Syria, and Yemen. Last but not the least, the Catholic Church, the main actor in my otherwise medieval puzzle, continues to be a major actor in international politics. It has taken sides in conflicts ranging from the Spanish Civil War to decolonization in Algeria, Cameroon, and Vietnam, in what Giuliana Chamedes depicts as “a twentieth-century crusade.”²⁶⁰ In all these cases, including a controversial role during World War II and the Holocaust,²⁶¹ the supranational hierocratic authorities rally their adherents (Catholic or Shiite religious actors, communists, etc.) against other local-national factions in their countries (e.g., fellow Cambodians, Iraqis, Spaniards, or Syrians) in civil wars. To the extent that these supranational hierocratic actors succeed, such efforts result in religiously or ideologically more homogeneous polities, as they did in late medieval Western Europe.

Ethnoreligious cleansing in medieval Western Europe has broad relevance for future research. The religious homogenization of Western Europe indirectly shaped the demography of the Americas through colonization and discriminatory immigration and citizenship laws.²⁶² This historical legacy is still relevant to many political puzzles, including European integration—“Roman Catholicism, after all, is the religious community most straightforwardly supportive of the prospect of European unity.”²⁶³ I argue that this legacy helps to explain why non-Christians were stigmatized across Europe and why not a single Muslim or Jewish community survived from the medieval period in Western Europe. This finding is particularly consequential because the discourse of a “historically” Christian-only Europe is often deployed to marginalize Muslim immigrants. My argument is also relevant in discussing why the vast majority of Jewish populations shifted away from Western Europe and toward Eastern Europe and the Middle East during the late medieval and early modern period.²⁶⁴ Scholars should study the religious demography of Western Europe and the Americas as an outcome rather than as an exogenous factor. This article has attempted to explain the political origins of religious homogeneity in Western Europe, which will hopefully stimulate other scholars to address this puzzle of historical significance.

Catholic-Protestant conflicts of the sixteenth and seventeenth centuries are widely recognized as being of foundational importance to the rise of modern nationalism and the international system.²⁶⁵ For example, Andrew Phillips observes that “once the Habsburg bid for empire had in turn been defeated, European rulers sought to re-establish order in their own kingdoms through the forcible imposition of confessional conformity, conflating religious dissent with political treachery, and thereby condemning Europe to a century of violence.”²⁶⁶ Yet the equation of religious difference with political subversion already in the early thirteenth century, as explained in this article, suggests that a medievalist critique of modernist theories of nationalism and the international system may uncover proto-national and even nationalist elements in the religious homogenization of medieval Western Europe.²⁶⁷

The author thanks Tarik Cyril Amar, Umur Baqdaq, M. Steven Fish, Eliza Gheorghe, Aydín Gündüz, Francesca Jensenius, Ivana Jevtic, Erdem Kabadayí, Morgan Kaplan, Kerim Can Kavaklí, Matthew Adam Kocher, Jody LaPorte, Evangelos Liaras, John Mearsheimer, Yusuf Mercan, Harris Mylonas, Emma Rosenberg, Theda Skocpol, Rolf Strom-Olsen, Ronald Suny, Alexis Norman Wick, Anders Winroth, Jason Wittenberg, J. Nicholas Ziegler, and participants during presentations at the 2016 Midwest Political Science Association annual meeting, the 2018 European Academy of Religion conference, the 2018 Council for European Studies conference, the IE University, Bilkent University, and Koç University, and the anonymous reviewers for providing valuable feedback. The author also thanks Zsofia Bocskay and Yury Katliarou for their research assistance. An online appendix is available at https://doi.org/10.7910/DVN/XCG3OI.