Another relevant Terry Pratchett quote about war.
"People are always trying to kill each other. That’s why we invented the law. War is just the law in a different form — the law that says you have the right to kill, as long as you’re killing for the right reasons. And the right reasons are always the ones that make you feel better about yourself. The right reasons are the ones that make you feel like a good person. The right reasons are the ones that allow you to kill the other guy without feeling guilty. Because if you kill the other guy because he’s evil, then you’re not a murderer — you’re a hero. And if you’re a hero, you can’t be guilty. You’re just doing what you have to do."
– Monstrous Regiment