[DenisM]

The worst criminals in that war were the Communists

Stalin's purges predate 1941 when SU entered the war. So they aren't part of the same war, unless you also want to add the extermination of native americans to the list of WW2 crimes.

And what was wrong with the winter war? A plain old war of agression, sure, but I don't think there were any war crimes?

[dkimball]

The Winter War, like Manchuria, was a "crime against peace" by the standard of Nuremberg; that establishes that Stalin, like both Hitler and Hirohito, had launched a small aggressive war prior to WWII.

The purges were not part of the war any more than the Holocaust was part of the war (pointed out at Adolf Eichmann's trial: the continued prosecution of the Holocaust actively impeded the Nazi war effort, especially by clogging up the railroad network); but I wanted to make it clear that Stalin as well as Hitler exterminated large numbers of his subjects during his "reign."

[DenisM]

Well, "the crime against peace" is a single-serving "let's stick something on them" charge. US engaged in multiple aggressive conquests after WW2 without anyone even mentioning the word "crime" in a serious context. So aggressive conquest is a common practice, whereas civilian massacre is universally frowned upon - a big difference in my mind.

I can see how to tie holocaust to WW2 - the regime which perpetrated the former has then also started the latter. Stalin didn't launch the WW2, but then you can argue he did set it in motion with the Ribbentrop-Molotov pact making both the purges and the WW2 part of his empire-building. Good point, I agree.