What pope urban I's main reason for calling for the first crusade or war of the cross''?

Pope Urban II called for the First Crusade in 1095 primarily to aid the Byzantine Empire, which was under threat from Muslim forces, and to reclaim the Holy Land, particularly Jerusalem, for Christianity. He sought to unite Christians in Europe against a common enemy, invigorate faith, and offer a path for penance and salvation. Urban's call was also motivated by the desire to assert papal authority and strengthen the Church's influence in a fragmented Christendom.