A chauvinistic country should be ashamed to house foreign troops.
The pre-Josean period was still of a unified Goryeo, and pre-Goryeo period was of Three Kingdom period, that too was not a North-South divide in any sense (google the maps).
I believe world is random with some very lose continuations like languages but even that is malleable - Levantines are speaking Arabic, not the language of their forefathers (Syriac, Aramaic etc), similarly Brahmins of different regions have assimilated to the native cultures.
There are examples around the world - Canadian nationalism which incorporates both English and French speaking people, Swiss nationalism which incorporates German, French and even Italians, Lebanese nationalism which incorporates a diverse people both in ethnicity and religious beliefs, even South Korea have both Christianity and Buddhism without affecting any "nationalistic" Korean.
I think I write facts that are true to the best of my knowledge, you can correct me of course.
My pleasure.