Were the crusades really fought over religion?

Answer 1

The justification for the crusades began in 1009, when the Fatimid caliph of Cairo had the Church of the Holy Sepulchre in Jerusalem destroyed. His successor permitted the Byzantine Empire to rebuild it under stringent circumstances, and pilgrimage was again permitted, but many stories began to be circulated in the West about the cruelty of Muslims toward Christian pilgrims. However, there were, of course, many underlying causes.

The historical background included the Christianisation of the Vikings, Slavs, and Magyars. The relative stability of European borders now meant that there was an entire class of warriors who now had very little to do but fight amongst themselves and terrorise the peasant population. Previous actions against Arians and other "heretics" offered further historical precedents for the crusades, in a society where violence against unbelievers would be acceptable.

There was also an awakening of intense Christian piety and public interest in religious affairs, providing overwhelming popular support for the First Crusade and the religious vitality of the 12th century. And for Pope Urban II, a crusade would serve to reunite Christendom, bolster the papacy, and perhaps bring the East under his control.

So, the crusades were partly about religion, partly an outlet for the agression and ambitions of the nobles and landless knights, and partly about Church and papal ambition.