People who can answer this in detail (unlike me) will firstly take issue with the casualty figures. I assume 6 million is the number of Jews, so it doesn't count all of the other innocent civilians. There is debate about Stalins casualties as whether or not to count certain indirect causes of death attributed to him. Personally I've always thought that Stalin killed more innocent, but someone recently suggested Stalins death count is much lower today than previously though. Hopefully someone can clear this up with a detailed answer, or redirect to one.