You see, the way I see it is that yes people were the ones who caused the wars. But over what dispute? Whose religion should reign. Naturally, I believe that Christianity is the right one. But I'm not so sure I would go to war and slaughter thousands just to "prove" it. It's a human mentality to think "if we prove dominance, our thoughts win". The religion sort of "contaminated" or "diseased" the minds of the people. If you view Christianity as a relationship, then you see other faiths of being just a different relationship. And yes the basis of Christianity and any other form of (for lack of a better word) religious matter is faith, but you can have faith without having religion.
EDIT: And I'm not saying war is bad, it's just overused. And yes the Bible says God did send the Israelites to war, but not a numerous amount of times. He never called for needless, unrelenting, massacre.