Starting with finances.
IN THE STANDARD MODEL, the crusaders were imagined as second sons with no inheritance, as robber barons, as highwaymen, or as others with nothing to lose out to get rich on the fabled wealth of the Orient. More recently, historians have started to look at the surviving data (such a marvelous thought!) and have found that this was not the case.
The pilgrimage to the East was self-funded, for one thing. No one was paying the knight’s plane tickets. In fact, there were no planes!³ So everyone had to get there on his or her⁴ own.
Crusading was expensive, up to five times one’s annual incomes. (Louis IX’s Seventh Crusade⁵ in the mid-thirteenth century will cost more than six times the annual revenue of the Crown.) To cover the nut, knights and lords sold freeholds, settled property disputes at a disadvantage, liquidated estates, borrowed from relatives, submitted grant proposals, and maxed out their credit cards. This was so extensive that preparations for the First Crusade introduced considerable inflation into Western Europe⁶ and instigated a net flow of wealth from West to East. (So much for getting rich on the wealth of the East.) One of the reasons why the Fourth Crusade will get hijacked to Constantinople was that it will run out of money before it even gets rolling.
See those footnotes, there? They’re very readable, but I didn’t copy and paste them here– you’ll have to go read it at The TOF Spot.