The First Crusade (1095-1099) was in response to Seljuq conquests which threatened pilgrimage routes and Christian holy places in the Middle East. Prompted by an appeal from the Byzantime emperor Alexios Comnenus (1081-1118) at the Council of Clermont in November 1095, Pope Urban II (1088-1099) urged Catholic Christian warriors to recover the Holy Land.
The Times Medieval World. Rosamund McKitterick (Ed.) Harper Collins, 2003, pg 146.