The Crusades were various European military expeditions to free the Holy Land from Muslim occupation (or to reinforce the Kingdom of Jerusalem) that were sanctioned by the Church of Rome. These expeditions occurred during between the 11th century and the 14th century and were of significant impact to the development of both Europe and the Muslim world. Other "crusades" were launched against various heretical branches of the Christian faith in Europe itself.
One who participated in a crusade is now known as a Crusader, although in period this term was not used; instead they were referred to simply as pilgrims or euphemistically said to have "taken the Cross".
The crusades had multiple causes: Church reform, increased population in Western Europe, maintaining access to the pilgrimage sites of the Holy Land, and the growth of the idea of knights as soldiers of the church. The success of the early crusades was due partially to division among the people occupying the Middle East, the failure of later crusades from the division of European efforts.
Crusading was popular because Pope Urban II made a decree that killing non-Christians was not a sin, but in fact a form of penance; killing infidels in Christ's name, he claimed, guaranteed one a place in Heaven. Interestingly, Muslim leaders assured their people that killing the invading Franks likewise guaranteed access to Paradise, which may explain the particularly sanguinary and brutal nature of warfare in the Holy Land.
- The First Crusade was preached by Pope Urban II in 1095.
- The Second Crusade was preached by Pope Eugene III in 1145.
- The Third Crusade was preached by Pope Gregory VIII in 1187.
- The Fourth Crusade was preached in 1198 by Pope Innocent III.
- The Fifth Crusade was preached in 1216 by Pope Honorius III.
- The Sixth Crusade was the product of Frederick II, Emperor of Germany (Holy Roman Emperor) commencing approximately 1225.
- The Seventh, and final major Crusade was the work of King Louis IX of France, and departed Europe in 1248.
- The Eighth Crusade finished in 1270, having being fought mainly by mercenary troops as there was little land to offer as enticement.
The Crusade of 1101 was a dismal failure, and was little more than a second wave of the First Crusade that was poorly co-ordinated and resulted in three major European armies being defeated by Turks.