I don't usually use 'evil' to describe things but I don't know any other word to describe settler states and their tendency to massacre and torment people they stole their land from and gleefully brag about all the horrific atrocities they've committed/want to commit. Never before have I seen a group people that take more joy in the suffering of others than the kinds of people that want to wipe out entire societies and claim their land for their own.
This is the kinda shit where if you write villains that act exactly like this people will slam you for bad or unrealistic writing, but no, it would actually be perfectly in line with reality all things considered.
EDIT: ps I know me not good at writing things. Wish I can write my thoughts on this better, but I can't really get it into right now
I think there are lots of psychological things at play. Think about survivor bias and how shitty that is. It's those kinds of things that manifest themselves from individual phenomena into the societal realm as well that contribute to all of it.