"But what about the Crusades and Inquisitions and the Reformation? Huh, huh, What about those?" Well, I won't deny that there are travesties in history in the name of religion, (although we really are bad at history here in America these days and all of these periods really require a deeper look and not just a mere caricature from the History Channel, especially if you're going to form strong opinions on them that weight your view about things like well, God and eternity), but I will challenge the assertion that religion, properly understood, was the source of the violence. Now, there is a great deal of qualifying that is needed here. Unfortunately, I don't have the time to do this justice. However, I'll remind folks of the well documented stat that in the 20th Century we became incredibly effective at killing one another and did so on a previously unprecedented level. Between Mao, Stalin and Hitler, all of whom took up ideological banners that carried an explicitly atheist component, more people were killed in one century than all of the combined war-related murders in the preceding 19 centuries.
Meanwhile, we see people of faith coming together at an unprecedented level to together appeal to God for mercy and an end war.