There's nothing wrong with countries, and small countries too. Generally, empires are the problem. Disparate people groups cobbled together in unnatural ways don't produce a harmonious society*. Britain and France were terrible for trying it (see: Africa, Iraq, etc.). The Ottoman empire "rump" should have been butchered into smaller pieces. Hindsight is 20/20, as they say.
I don't think every country has genocided, but many certainly have. *That's what China is trying with the Uighurs.