But throughout history religions have notoriously aided and abetted our worst tendencies. To be sure, wars have been fought for non-religious reasons. Probably most if not all. It's an interesting question because humans, like all animals, have an instinct for survival, and charging headlong into a barrage of bullets and cannon fire is a counter-intuitive, and basically stupid thing to do. Yes, there are atheists in foxholes, but they at least fully appreciate their predicament.
Death is death.
In trying to imagine a world without religion, we have to imagine, for a start, a world that never engaged in any of the above mentioned religious wars and inquisitions. Think of it. All that killing and torture would never have happened. Holland was a magnet for scientists, philosophers, artists and merchants. While Rome was threatening Galileo with the tortures of the Inquisition for his heretical observation that moons orbited Jupiter, Protestant, tolerant Holland beckoned with enlightenment.