The Crusades were penitential war-pilgrimages fought in the Levant and the eastern Mediterranean, as well as in North Africa, Spain, Portugal, Poland, the Baltic region, Hungary, the Balkans, and Western Europe. Beginning in the eleventh century and ending as late as the eighteenth, these holy wars were waged against Muslims and other enemies of the Church, enlisting generations of laymen and laywomen to fight for the sake of Christendom.

Crusading features prominently in today's religio-political hostilities, yet the perceptions of these wars held by Arab nationalists, pan-Islamists, and...