I'm making a shortcut here and I assume all wars have a religious motive in their essence. Maybe it's not even an assumption :-)
But imagine religion didn't exist. What would we hate each other about and use as an excuse to fight ?
Ive made a small list :
- Race : always a good one. You are black, i dont like you
- Region : I dont like people living in that area lets kill them. Maybe difficult with historical migration
- Social status. Maybe difficult to determine
- Football club. I like this one
- ...
You see easy to find some reasons :-) All of them as stupid as the current reason of most wars !