Well hell, MM sure knows how to get the people going hey? This is a juicy topic, we've got people at each others throats over history and religion, now let's throw in the race card and really stir the pot!!!
Seriously though...
I hate to break this to you but more people have been killed in the name of G-d than any other reason.
See this is a really touchy subject. Stepping back and taking a look at the bigger picture,
people kill for the dominant belief system of their time Now, oftentimes in the past this meant a religion, but more recently has been political causes and the like. Let's pretend that christianity never became incorporated into the state (which is what the Roman emperor Constantine did) and that it was carried forward as a purely non-political body. If that were the case, the powers that be at the time would have used another mechanism to get people fired up to go and kill.
The crusades, for example, were largely about political control and gaining as much wealth as possible, it was a means for medieval Europe to try it's hand at empire building like the Romans had done in the past. However, the average king couldn't very well go out to his subjects and say
"hey guys, I know you're dirt poor but I want to have more land and power for my family line, so how do you feel about leaving your entire life behind to go and kill other poor people for my benefit? Oh, and, by the way the chances of ever seeing your home again are so-so at best!"
So, they took a political cause and wrapped it in the cloth of religion. Liberating the holy land from the saracen scourge of course! Many of the nobles and monarchs that embarked on the crusades DID believe that they were doing the work of God, but that essentially means that they bought into the big lie, or even worse started believing the lie that they were perpetuating.
And then you have the many, many atrocities that were committed by the conquistadors and good, "God-fearing" pilgrims when they came to the new world. Never mind what they did, it was just a few savages who died, right?
Once again, recurring pattern.
People will always kill for the dominant belief system of their time I remember the Japanese were mentioned, during WW2 they fought with fanatical zeal, and believed fervently in their perfect emperor and the infallibility of their empire. And the Germans in WW2, not to mention the Russians all willingly threw themselves into the grinder. In WW1 especially many fine English chaps gladly signed up to go across the channel and get mowed down in idiotic frontal attacks on trenches... but glad to do our part for King and country, God save the Queen! During the cold war people gladly went to kill and be killed in the name of fighting off the godless commies.
So, what is the excuse being used today, hmmm? Perchance it could be "The War on Terror", which really is brilliant, because that means that you can technically be at war with any and every group of people on the planet (including your own citizens, because they can turn into terrist scum to ya know!) in perpetuity. Bravo!