Think of them as IRL containment threads - the members of nations can exert their own laws, customs, culture, language, political or religious beliefs without imposing them on the rest of the population, causing conflicts and shit-flinging festivals. It worked fine (except 17th century, where euroids were at constant war with each other, and both World Wars), until the virus of multiculturalism has been planed in minds of elites. Such utopia is hard, if not impossible to maintain, ethnic conflicts are due to happen. Yugoslavia showed that to outside world.
Most of the time you need to wall yourself away from retards on the opposite side. So that retards will have harder time getting on your side, and also so you don't get to see the utter repulsiveness of their antics, making you MATI. And trying to integrate retards into civilized discourse, look at both African former colonies and nigger-loving eurocuck countries that accepted illegal rapefugees en masse. How did it end up? First group is still almost all shitholes, second... well many countries are backpedaling on that matter, and more right-wing, anti immigration parties are gaining traction. Which further proves my point.