WRT Japan: the first time that I bought a history book on Japan and got it home and read it, I was surprised to find that WWII -- and the occupation of China that preceded it -- took up all of about 5 pages
Yeah, I think you're on to something with your question about the victors getting to write history... but more to the point, it was the atrocities themselves that lent the final psychological justification to a war for those Allies on whose ground the war was
not being fought -- i.e., the US, Canada, Oz, etc.