However, Ubaidah was respectful to the Patriarch of Jerusalem in 637 and didn't accept his invitation to pray in the Church of the Holy Sepulchre for fear that his followers would later tear it down and turn in into a Mosque because he had prayed in there. Due to that the Church of the Holy Sepulchre has continued to stand as a Christian temple since. Meanwhile the Temple on the Mount was built in place of debris and rubble that had not been cleared since the sacking of the original temple by the Romans. Also the Byzantines were the remnants of the Roman Empire who had conquered Jerusalem from the Jews centuries ago but that wasn't for religious reasons either. The result is that the crusades were never a war of religion but of land and politics.
The Romans took Jerusalem from the Jews.
The Muslims took Jerusalem from the Byzantine empire (the successors of the Roman empire).
The Crusaders took Jerusalem from the Muslims and didn't return it to the Byzantines as promised and instead kept it for themselves.
The retreat of the Crusaders after two centuries allowed the Muslims to take back Jerusalem.
Nowadays Israelis and Palestinians dispute who owns Jerusalem and war still occurs in the Middle East once again for land (and apparently oil).
The Crusades were often seen as religious holy wars but they were pseudo-religious with the main motivation being land, power and money. Crusaders simply fought they were fighting for God and the Church yearned them on. In truth they were fighting for rich nobles and it's no different from today's wars. Atheists really should take some history lessons.