Answer:
Pope Urban launched the First Crusade in 1095 after the Council of Clermont. During that council, the dire situation of the Byzantine Empire was analyzed: the Byzantines were being invaded by the Seljuk Turks who were making great military progress in Anatolia, and as the Byzantines were a Christian people, Pope Urban urged to aid in their defense.
He called out for noble warrios to embark to the Holy Land and other regions of the Middle East, and recover those lands from their Islamic rulers. In exchange, he promised forgiveness for any past sins that the crusaders had commited before taking up arms to defend the church and the Empire.
