Generally, the population in Europe during the Middle Ages was divided into castes, or as it was called in France, “estates.” The first estate was knighthood, the noblemen. The second estate was the clergy. The third estate was the commoners, and then there were the peasants or serfs who were not even an estate.
The knights were trained for war. Therefore, they could not exist in a time of peace. They were completely non-productive unless they were fighting. Consequently, Europe was in a constant state of war. These wars had nothing to do with the public good, logic or even money. The phenomenon of ever-warring knights had taken on a life of its own. Besides needing war, every knight needed horses, servants, pages, squires… and had to throw a banquet virtually every night. It was its own self-perpetuating industry.
The constant wars sunk Europe into the throes of virtual chaos. Villages were regularly sacked. The men were killed, the women were raped, the children were sold into slavery and all the plunder that could be taken was taken.
That is one of the reasons that a Crusade was such a good idea. The Pope wanted to get the knights out of Europe. It was essential to move them away somewhere. The Crusades was a perfect answer. It solved so many needs at one time.