The Crusades War started due to many reasons. One reason was the Christians thought that the rise of a new Muslim leader was a threat. They assumed that Muslims would then attack and steal from them, in which they did by capturing Jerusalem. The Christians then felt unsafe there as they were attacked while the Muslims took over. Another reason is after this threat, Pope Urban the Second was commanded to take the Holy Land back. The Byzantine emperor feared that the Muslims would take Constantinople after taking Jerusalem because they were already starting to invade the empire. Finally, Pope Urban called for all Christians in Europe to help him take it back. Many came because they wanted to save their souls, do what they thought God wanted them