Question

Pope Urban II called on Europeans to join a Crusade against

Answer 1

I believe that the most fitting answer for this question would be that the Crusades were called to fight against the Muslims. In 1095, the Pope claimed that Muslims were destroying the Holy Land and called on European Christians to put an end to it. They sought to regain control over Jerusalem. 

Answer 2

Answer:

The Muslims

Explanation:

Pope Urban the II called the Crusades against the Muslims as an act of taking back the Holy Land, Jerusalem. Pope Urban told the people that he was the mouth piece the God and or ´Victor on Earth.´ Pope Urban also promised his people that they would gain salvation if they fought for the Holy Land.