Christianity?
Yes, I suppose it is behind many wars. War needs an excuse: sometimes it is revenge; sometimes politics; sometimes ideology; sometimes ethnicity; sometimes greed or sometimes religion.
The triggers behind war are usually very complex. Religion is rarely the real motivator, but defines the excuse. The perpetrators need to feel justified.
War is rarely declared in the name of one's own prejudice or revenge. We need to justify our actions with a 'just cause'.
It's difficult to imagine the Jesus who taught his followers to love their enemies, approving of the medieval crusades. He did not fight back when they came to arrest and crucify him. Would He approve of murder and rape?
If religion were completely removed from the world then we'd still find a reason to hate each other. We'd rally to some political cause or ideology to justify our greed, revenge or hatred.
Whilst religion has been used as an excuse for evil, it has also motivated many to good. William Wilberforce was motivated by his Christian Faith to see slavery abolished. Mother Teresa gave her time, energy and life to the poor because of her Christian Faith.
Further Research
Christianity FAQ