During World War II, Japan was short of people to work in some industries, so deported some Korean Families to Sakhalin Island (the southern half was part of Japan then). Wikipedia has a page about them: a complicated history.

So one video posted today on KBS World is about the cultural and language problems of those who have more recently moved back to Korea.

a lot of the difficulties are the same for immigrants in many nations, and I posted this mainly as an example of how history has complicated the idea of nationality.