This is a general overview since the question is a little broad. If you have specific follow up, someone with military flair might need to jump in.

This year, the People's Republic of China will be celebrating their 70th anniversary of the defeat of Japan. Of course, the whole thing is a lot less simple than that.

WWII was in Asia effectively a continuation of the Second Sino-Japanese War which had been going since 1937 (or 1932 depending on what you want to call the beginning).

"Political stance" is also a little complicated. During this period, China was also in the midst of their civil war, with fighting not only against the Japanese (largely on the part of the Kuomintang) but also between the Kuomintang and the Communists. The civil war lasted through the 40's, years after the end of WWII.

There were a lot of discipline and logistical problems in China at the time, which led to greater casualties than what it could have been, and that's part of what you're seeing with those numbers.

China was very much involved during this period, starting before and ending after the war in Europe.