Japan actually invaded, what Manchuria, China in the early 1930s, 1932.
At times, I wonder if that invasion caused, in part at least, that area of Asia to hemorrhage for years afterwards.
But then, you had Communism on the move as well and that caused great hardship. Great Leap Forward and the Cultural Revolution but who knows, maybe without the Japanese invasion, the rulers of Japan, Chiang Kai-Shek(?) or Emperors would have been able to quell Communism. Obviously, it's a complex matter. One would need to get the history books out.
Yes, the Japanese believe in a very homogenous society but look at them now, I guess they are having problems keeping the birth rate up; a bit off-topic.