Why China Korean community population of 2 million people?
They prefer to not become the Japanese name and sintoism conversion, and flied away from Japanese occupation.

But before of this, Koreans escaped from Korea in front of hard economic situation. Other are people displaced for forced works.
What fit not in this number?
The Japanese army was destroyed in 1945. Why Koreans returned to their homeland? Some time was the devastation is clear. Then the war with the Americans and again devastation and now prevents? I have to say. They do not like and do not support Kim. It is better to live in poverty in China than return to North Korea.