In my home galaxy, humans weren't the only sentient beings that existed - though I know that's how it is here for most. I'm afraid that, at least where I'm from, humanity wasn't the only race stricken with the need for war and destruction. It was more or less commonplace amongst all sentient lifeforms, except perhaps for droids - unless they were under the command of others who mobilized them into armies.

Here, it seems more due to restriction, boredom, and fear of the inevitable. Like somehow killing a bunch of other people is going to somehow transfer over to the killer and make them live longer.