What was pope urban main reason for calling the first crusade or war of the cross?

Pope Urban II called for the First Crusade in 1095 primarily to reclaim Jerusalem and the Holy Land from Muslim control. He aimed to unite Christendom and provide military support to the Byzantine Empire, which was under threat from Turkish invasions. Additionally, the pope sought to restore the authority of the Church and provide a spiritual incentive for participants, promising forgiveness of sins for those who took part in the campaign.