The japanese were waging a war in China way before the second world war(1937). It was quite a brutal and bloody war on a massive front.
The nationalist Chinese were getting a bit of a drubbing, then the yanks started helping a bit via volunteer groups. The Chinese communists were in a seperate state, in the mountains (iirc) and they had been fighting the nationalist chinese since the mid 20's.
the whole bunch of them were brutal, viscious and nasty