Soon after liberating the ancient Christian city of Antioch from Muslim oppression, the First Crusaders managed in 1099 to realize their primary goal: take Jerusalem from Islam. Despite all the propaganda that surrounds the conquest of Jerusalem, there were very few Muslim calls to jihad (only one is known, and it quickly fell on deaf ears). After all, in the preceding decades, and thanks to Sunni and Shia infighting, local Muslim populations were hardly unused to such invasions and bloodbaths. In Muslim historian Ibn al-Athir's words, "[w]hile the Franks — Allah damn them! — were conquering and settling in a...