Genocide is basically the worst of the war crimes. It's worse than ethnic cleansing because the intention here is simply to drive a population from a territory, usually by means of brute force but it's a step down from genocide where you're not even giving them a genuine chance to leave. Genocide, that's where you round up Jews, gays and anyone else you don't like, and gas them. That's not trying to drive a population away from a territory, that's a clear policy to exterminate people based purely on their identity.

Ethnic cleansing is something many people might be turning a blind eye to, if and when Ukraine retake Crimea and evict the Russian population. You might want to be careful what moral standards you set right now, because the side you support might well have to cross those lines too if they are to achieve their military objectives.

War is shit.