War is inevitable because man is territorial. We want to own land and we want more of it. We also want to hold onto what we have. So of course, there will be war over land.
Then we also have almost an instinct to believe in something to justify our existence. Most of the time that takes a religious form. More wars have been fought over religion than any other reason. More have died for that reason.
You can just search by religions or wars in countries. There is plenty of material.