The Crusades were a series of religious expeditionary wars blessed by the Pope and the Catholic Church, with the stated goal of restoring Christian access to the holy places in and near Jerusalem. The Crusades were originally launched in response to a call from the leaders of the Byzantine Empire for help to fight the expansion into Anatolia of Muslim Seljuk Turks who had cut off Christian access to Jerusalem, and were also sparked by the destruction of many Christian sacred sites and the persecution of Christians under the Fatimid caliph Al-Hakim. The crusaders comprised military units of Roman Catholics from all over western Europe, and were not under unified command. The main series of Crusades, primarily against Muslims in the Levant, occurred between 1095 and 1291. Historians have given many of the earlier crusades numbers. After some early successes, the later crusades failed and the crusaders were defeated and forced to return home.

Several hundred thousand soldiers became Crusaders by taking vows; the Pope granted them plenary indulgence. Their emblem was the cross — the term "crusade" is derived from the French term for taking up the cross. Many were from France and called themselves "Franks," which became the common term used by Muslims.