The First Crusade was launched by Pope Urban II at the Council of Clermont in 1095.

A key trigger was an appeal for military aid from the Byzantine Emperor Alexios I Komnenos against the Seljuk Turks.

The Seljuk Turks had conquered most of Anatolia and were also making it difficult for Christian pilgrims to visit the Holy Land.

Pope Urban II's motivations included increasing papal authority, healing the schism with the Orthodox Church, and redirecting the violence of European knights outward.

There was intense religious fervor in 11th-century Europe and a popular desire to liberate Jerusalem and the holy sites from Muslim rule.

The Pope offered a plenary indulgence, the complete remission of sins, to those who went on the crusade.

Economic and social motives also played a role, as landless younger sons of the nobility saw an opportunity to acquire land and wealth.

The Peace and Truce of God movements had sought to limit warfare within Europe, making a foreign expedition appealing.

Charismatic preachers like Peter the Hermit mobilized large numbers of common people.

The crusade was a complex phenomenon driven by a mixture of religious piety, political ambition, and economic incentives.