Causes of the Crusades: Why the Holy Wars Began

The Crusades did not erupt from a single cause. They were the product of decades of religious, political, economic, and social pressure in both Western Europe and the Mediterranean world. To understand why hundreds of thousands of Christians were willing to march thousands of miles to fight in lands they had never seen, one must consider a constellation of causes that converged in the late 11th century. The older “pluralist” answer — that religion, economics, and politics each played a part — has been challenged since the 1980s by Riley-Smith and his students, who argued that the religious motivation was primary and that the other factors were the occasion, not the cause, of the expedition. The argument has not been settled, and a fair summary of the current state of the question is that religion was the necessary cause, the others were the sufficient ones, and the expedition would not have happened without both. This article surveys the principal factors.

For the broader context, see the main article on the Crusades and the Timeline of the Crusades.

Religious Motivations

The most often-cited cause is religious. By the 11th century, pilgrimage to Jerusalem was a deeply embedded spiritual practice. The disruption of pilgrimage routes by the Seljuk Turks, and especially the capture of Jerusalem in 1076, generated a sense of outrage in Western Christendom. The papacy, freshly empowered by the reform movement of the 10th and 11th centuries, was quick to mobilize this sentiment.

The appeal of Urban II at Clermont in 1095 offered unprecedented spiritual rewards. Those who took the cross were promised remission of sins, protection of their property, and a privileged place in heaven. For more on the religious appeal, see the discussion of the First Crusade.

The Byzantine Appeal

In March 1095, the Byzantine Emperor Alexios I Komnenos sent an appeal to Pope Urban II for military assistance against the Seljuk Turks, who had been steadily advancing through Anatolia since the catastrophic Battle of Manzikert in 1071. The Byzantine request gave the papacy both a pretext and a strategic opportunity. Without Alexios’s appeal, the First Crusade would not have taken the form it did.

The Reform of the Papacy

The 11th century saw a profound transformation in the papacy. Reformers such as Gregory VII sought to free the Church from secular control and to assert papal supremacy over temporal rulers. The Crusades offered the papacy a means of directing the military energies of the lay nobility toward ends that enhanced papal prestige. The papacy’s role in calling the First Crusade and in preaching the Second Crusade reveals this strategy clearly.

Western Europe in the 11th century was a violent, hierarchical society in which a small warrior elite dominated a much larger peasantry. The nobility lived for warfare and land; both were in increasingly short supply by 1095. The fragmentation of inheritance, the growth of primogeniture, and the conversion of benefices into hereditary fiefs had produced a class of landless knights, the milites, who had more to gain from military adventure abroad than from further conflict at home.

The Church cleverly offered these knights a way to earn salvation and riches at the same time. The result was an unprecedented response to the call of Clermont.

Economic Pressures

While historians debate the importance of economic motives, the medieval economy provided many incentives for participation. Italian maritime republics like Venice, Genoa, and Pisa saw commercial advantage in the establishment of Crusader States in the Eastern Mediterranean. Younger sons of noble families could hope to acquire land in the new Crusader principalities. Even commoners might escape debt and bondage through the expedition. The role of the Italian merchants is especially clear in the Fourth Crusade, where Venetian commercial interests effectively shaped the entire campaign.

The Seljuk Threat

The expansion of the Seljuk Turks through the Middle East, culminating in their capture of Jerusalem in 1076, was the immediate trigger. The Seljuks were not uniformly hostile to Christian pilgrims, but the breakdown of central authority under their fragmented emirates made the pilgrimage routes dangerous. Stories of persecution, possibly exaggerated, circulated in the West and helped to inflame opinion.

The Seljuk threat also brought the Crusaders into contact with formidable Muslim leaders, most famously Saladin, whose unification of Egypt and Syria in the 1170s and 1180s would transform the character of the Crusading movement.

The Papacy’s Agenda

Pope Urban II was a Frenchman, a former monk, and a skilled politician. His agenda at Clermont was complex: to aid the Byzantines, to assert papal authority, to redirect knightly violence, and to enhance the prestige of the Latin Church. The Crusades served these goals simultaneously. The papacy’s repeated inability to control the movement once it began, however, would become a recurring theme of the next two centuries.

The Crusades were caused by a unique convergence of religious enthusiasm, papal ambition, Byzantine appeal, social pressure on the Western nobility, and the military situation in the Eastern Mediterranean. No single factor explains the movement; each was necessary, and together they produced one of the most remarkable military mobilizations of the medieval world.

To explore how these causes played out, see the First Crusade, the People’s Crusade, and the causes and consequences of the Council of Clermont.

The Background of the Late 11th Century

To understand the Crusades, it is essential to see them in the context of the late 11th century. Western Europe had been transformed by the previous century of reform and recovery. The Viking, Magyar, and Saracen invasions that had plagued the early Middle Ages had largely ceased. The climate was relatively warm and the population was growing. The great monastic reform movements, especially the Cluniac and Cistercian, had renewed religious life. New cathedral schools were emerging in France and Italy, and there was a sense of energy and possibility across Christendom.

At the same time, Western Europe remained a violent and fractious society. Feudal warfare between petty lords was endemic, and many knights lived by plunder. The Church had long struggled to redirect this violence, most famously through the Peace of God movement, which sought to limit fighting against non-combatants. The Crusades can be seen as the culmination of this long effort: an attempt to channel the energies of the warrior class against external enemies rather than against each other.

The Byzantine Context

It is important to remember that the Byzantine Empire in 1071 was still a major power, even after the disaster at Manzikert. The emperor Alexios I Komnenos was one of the most capable rulers of his age, and he was actively campaigning to recover Anatolia. His appeal to the pope was, in some ways, a desperate move; in other ways, it was a calculated gamble. The Byzantines had used foreign mercenaries before, and Alexios may have hoped to recruit Latin knights without ceding Byzantine independence.

What he got, of course, was something quite different. The First Crusade produced not a client army but an independent force with its own objectives. The relationship between Crusaders and Byzantines was uneasy from the start, and it would only deteriorate over the next century. The Fourth Crusade finally destroyed the relationship entirely.

Religious Enthusiasm and the Apocalyptic Mood

One of the most striking features of the Crusade movement is the genuine religious enthusiasm that underwrote it. The response to Urban’s call at Clermont was far beyond anything the pope had anticipated. People of all social classes, including women and children, were willing to abandon their homes and march thousands of miles to fight for the Holy Land. The apocalyptic mood of the late 11th century, with widespread expectation of the end of the world, gave the Crusade a sacred urgency that surprised even its promoters.

The success of the First Crusade reinforced this mood. The capture of Jerusalem in 1099 was widely seen as a providential event, and the relics that the Crusaders brought home to Europe only intensified the religious energy. Bernard of Clairvaux’s preaching of the Second Crusade drew on this same well of enthusiasm, though with far less success.