For philatelists interested in the subject of “Korea” the link between Koreans living in the former Soviet Union and philately has to do mainly with the subject of mail sent to (North) Korea from Sakhalin. Until 1945 the south of the island was part of the Japanese empire and when the Japanese evacuated the southern halve in panic they abandoned the Koreans who had been part of the work force imported by Japan to work in the mines.
But that is not the only example of ethnic Koreans living in the Soviet Union. There was an earlier and much larger group of Koreans living in the USSR. They are the Корё сарам or Koryo-saram (Korean: 고려사람). Today they number approximately 500.000 people, most of them living in Russia and Kazakhstan but also in other countries which were at one time part of the Soviet Union.