Worth pointing out: the Crusades were largely a response to the constant Muslim attacks and invasions on Christian soil. The "Holy Land" had been Christian territory 400 years prior, Muslim slave ships regularly sacked the Mediterranean coast looking for European slaves (the original castles were built up in the mountains to protect from Muslim pirates), and Muslims had already invaded and setting in Spain/Portugal, and had just before the Crusades Muslims had been repelled out of Italy. It's a good thing we had the Templars for as long as we did, and it's unfortunate they couldn't maintain control of the area.