Fighting Japan (a neighboring country that constantly was at odds with China) pre-WWII is not the same as fighting in WWII. They essentially just continued a war they were already in.

France is an exception, but once France was liberated they fought once again. And they were one of the first to be invaded so you can't really fault them for being a victim to Blitzkrieg. The Russians and Americans also fought the war in both theaters. The English and the French both sent troops to fight Japan so I'm not sure where you're getting your info from.

Also not to mention the CCP was doing nothing to help and was undermining the government during the conflict for their own power.