Crusading kings such as Louis IX of France and Richard I of England exert a unique hold on our historical imagination. For this reason, it can be easy to forget that European rulers were not always eager participants in holy war. The First Crusade was launched in 1095, and yet the first monarch did not join the movement until 1146, when the French king Louis VII took the cross to lead the Second Crusade. One contemporary went so far as to compare...