Many Historians agree that the main cause for the Pope giving the ceremony was a messenger from the Byzantine Emperor Alexios Komnenus asking for help against the Turks who were now knocking on the doors of Constantinople. He had asked for a batch of 6000 highly trained knights from Europe to be stationed in Constantinople, in return for adopting Catholic Christianity in place of Orthodox Greek Christianity (Shepard 107)
It was a brilliant opportunity for Pope Urban to reassert Papal authority, and the Byzantine Emperor asking for help was the perfect opportunity. If he could successfully arouse the people to arms against the Muslims, Catholic Authority would be strong for at least another 300 years. This would also cement the growing fissures in the Catholic Church (Munro 231)
Knowingly or unknowingly, the Pope had set off a chain of events that would drag Europe out of its Dark Ages and would also split the Catholic Church into dozen other factions.