The crusaders were thugs, who were largely out for loot. When the First Crusade assembled, the first thing they did was have a pogrom against Jews in Germany. That set the tone for the whole of the crusades. When they got to Jerusalem, the leaders of the crusade promised the Jews and Muslims that they would be left alone if they surrendered, and then slaughtered many of them.

The sole accomplishment of the Fourth Crusade was the sack of Constantinople, which led to the fall of the Byzantine Empire.