Debating the Role of Religion in War

To the Editors (Ron E. Hassner writes):

Michael Horowitz’s compelling article deserves praise for pushing the agenda on religion and war beyond two contemporary obsessions: the fixation on religion and nonstate violent actors, particularly insurgents and terrorists, and the emphasis on Islam as the primary religious movement associated with violent conflict.¹ By examining how religion affected the duration of the Crusades, Horowitz persuasively demonstrates that religion has also shaped the behavior of conventional, Christian military forces.

This is a step in the right direction, but it is an all-too-cautious step. Because Horowitz overemphasizes the narrow, causal effects of religion, at the expense of exploring the manifold ways in which religion can pervade and constitute all aspects of warfare, his argument suffers from endogeneity and missing variable bias. As I show below, these difficulties result in an argument that both overstates and obscures the primary effects of religion on war. Historical analyses such as these distract from what should be scholars’ primary concern regarding international security and religion: exploring the role of religion in contemporary interstate war.

Endogeneity and Missing Variable Bias

Horowitz argues that it was religious fervor that drove the Crusaders to continue their campaigns long after the costs exceeded the benefits. Religion shifted “individual- and group-level calculations about the utility gained from continuing to fight”; thus “religion played an important role in extending the Crusades” (pp. 170, 180). Horowitz may have the causal story backwards: the duration of the Crusades might have affected the religious fervor with which they were fought. As the evidence of growing failures and insurmountable obstacles increased, the Crusaders would have turned to religion for reassurance and ex post justification of their enterprise.

How might one tell apart these two accounts in which religion drives duration or duration drives religion? Horowitz’s documentation of the rituals and beliefs that accompanied the Crusades fails to resolve this dilemma. The miraculous discovery of the Holy Lance in Antioch may have been the factor that motivated the Crusaders to ultimately defeat the Muslims besieging the city. Alternatively, the charismatic monk Peter Bartholomew might have felt compelled to produce the lance after a majority of the besieged Crusaders deserted the city and the rest, at the brink of starvation, prepared to surrender.² Perhaps the Crusaders fasted and circumambulated Jerusalem in a barefoot procession on July 8, 1099, because they believed the divine vision reported by Peter Desiderius, who promised the imminent collapse of the city walls. Or they might have participated in this ceremony because shortages in supplies, severe losses in manpower, infighting among the various contingents, and a failed assault on the city on June 13 necessitated a cooperative ritual. The unusual ceremony failed to bring down the walls around Jerusalem, but it did lead to a public reconciliation between the different Crusader factions, which then launched a coordinated and successful assault on the city five days later.³

One way to resolve the endogeneity conundrum is to investigate whether religious fervor declined over the course of the Crusades. If, as Horowitz suggests, religion provided an initial stimulus that fueled the Crusades, then religious enthusiasm should have ebbed over time as the Crusaders came to exhaust the ideological capital that religion provided and grew disillusioned with the religious rationale behind their actions.

The history of the Crusades provides no indication of such a decline in religious enthusiasm. Crusaders continued to cite religious motivation well into the fourteenth century and, even as they were turning on their coreligionists, employed religious language and justifications to rationalize their actions. The miraculous apparitions associated with the First Crusade, such as the celestial vision of St. George and the discovery of the Holy Lance, found their matches in subsequent campaigns, if reports from participants are to be believed. The knights of the Fifth Crusade marched into battle behind priests carrying the True Cross. On the eve of the Sixth Crusade, “a luminous crucifix, with the marks of the five wounds of the Saviour, appeared suddenly in the heavens [which] greatly inflamed the enthusiasm of the people”; in...