The Crusades had a lot of religion in it, they battled not with guns, but with swords, they were using armor and horses like in the dark ages. The Europeans were the people who where the knights, they fought other knights from other cities, the dark ages and most of the crusades were started by the Europeans. The crusades were started by the popes, they start fighting other cities that have a different religion then they try destroying all the cities with different religions so that all the people in the world are that religion but if that happens someone other people will just create other religions then the other people might also be in that religion then there are other religions again so it was kinda a stupid idea because at the end there would be other religions because other people made them and that is why it was kinda stupid.