When Alexius I Komnenoi implored the pope (Urban II) for help, he meant it to reconquer the lost Byzantine lands (and therefore return in to their de facto ruler, a.k.a., the Byzantines). Urban however, decided to merely use that as a façade in order to then invade the Muslims, and retake the holy land.
He also saw the wanted to unite Christianity as a whole (All the sects at the time, Orthodoxy, Catholicism, Paulicianism, Iconoclasts, etc. into a single conglomerate, fighting a common enemy.)
Pope Urban the II wanted to get back the Holy Land in which had been over taken by the Muslims at the time. Having the Holy Land was some what of a pride thing since Islams, Muslims, and Christians alll use it for their Holy Land.
