The pivotal event that occurred in 1095 signifying the launch of the Crusades was Pope Urban II's call to arms during the Council of Clermont. He urged Christians in Europe to take up arms and reclaim the Holy Land, particularly Jerusalem, from Muslim control. This call marked the beginning of the First Crusade, which aimed to unite Christians and expand Christendom. Urban's rhetoric emphasized the spiritual rewards of participating, including the forgiveness of sins. This mobilization led to a series of religious wars known collectively as the Crusades, shaping medieval European and Middle Eastern history over the subsequent centuries.