What were the effects of the Crusades domestically? I’ve heard the argument that it speeded up centralization as nobles were weakened, but how true is this? We’re the Crusades primarily a foreign affairs that had little affect on the people at.home in Christian Europe?

I mean, it weakened plenty of kings, when you think about Barbarossa drowning in the Saleph river, or Richard the Lionheart bleeding land and gold while held captive by Leopold of Austria and Holy Roman Emperor Henry VI, or sainted Louis IX of France losing his army, his liberty, and a third of his annual income at Al Mansurah, and then following up that disaster by dying of dysentery at Tunis. So it was something of a mixed bag.  

I would argue that the Crusades had profound effects on the people at home: the People’s Crusade and the Children’s Crusades saw thousands of people on the march, there were massacres of Jews in the Rhineland and widespread banditry on the march to Constantinople, the Italian city-states boomed as they replaced the Byzantines in the Eastern Mediterranean, Western European culture was profoundly shaped by their contact with both the Eastern Roman Empire and the Muslim world’s preservation of Greek and Roman philosophy, contributing immensely to the Renaissance.