dismissing the concept of ethnicity may be appealing in the Western bubble but you will find few takers in the rest of the world.

to reduce the NK situation to "they won't let anyone go" is also disingenuous. even if you ignore that the US refuses to allow any more meaningful peace so it can justify a continued military presence halfway across the globe, the US and South Korea are clearly more powerful and wealthy. clearly they are in a better position than NK to make concessions and pave the way for integration.