What jesus taught, obviously wasn't learned very well. If I remember correctly the crusades included those who believe in christianity? How about the Inquisition, more religion killing in the name of god. Hell the folks in the middle east of the same religion are killing each other because on side isn't practicing Islam in the right way. So what god taught and man learned is two completely different things.
And who's fault is that? Put the blame on the people, not God...