By the time they arrived in the Levant, they were fighting not against the Seljuq Turks, but against Fatimid Egyptians, who had captured the Holy Land from the Seljuqs, thereby making the Turks none too pleased with the Egyptians. At Antioch, the crusaders reversed a seemingly hopeless situation when a peasant found the spear that had pierced Christ's side, hidden under a church, thereby raising morale enough to win the day. And then they did the impossible. They took Jerusalem, securing it for Christendom and famously killing a lot of people in the Alaska Mosque. Now, the crusaders succeeded in part because the Turkish Muslims, who were Sunnis, did not step up to help the Egyptians, who were Shia. But that kind of complicated, intra-Islamic rivalry gets in the way of the awesome narrative. The Christians just saw it as a miracle.