The Crusades were fought because the Turks took Jerusalem and the French wanted the holy city back so Pope Urban II asked for all the French citizens to attack the Turks at Jerusalem to get the city back.Most sad no so the Pope told the citizens it was gods will. It took 2 years for the citizens to get ready.The peasants or slaves couldn't wait so they went to Jerusalem all by themselves to fight but were all shot down in less than day. After that he citizens went to fight and they won. Then Saladin of Egypt wanted Jerusalem and they lost to him. Then all the kids that were still in France all went on a trip to Palastine to fight. On their way there a man told them he would take them there but sold all the kids in to slavery. Then some kids from Germany went to Palastine to fight but all died of disease or died of starvation. And those were the crusades.
Cause they wanted to ?
Christians believed thier religion was god's religion,the muslims believed thier religion was god's religion so they got together and slaughtered each other in the name of god
People back then were morons and didn't know any other way to get what they want other than to fight. Simple as that.