Terry Teachout has a very important post at Contentions. Here’s just the first paragraph:
Why are so many Americans unaware that Joseph Stalin was as brutal, systematic and effective a killer as Adolf Hitler? One reason is because so much of the Old Left looked the other way at Stalin’s nefarious activities, and was unwilling later on to admit that it had done so. Another is that the Soviet Union remained a closed society long after the killing stopped, making it vastly more difficult for interested Westerners to study the Great Terror in the way that the Holocaust became a subject of detailed historical inquiry. As a result, we know far more about the individual innocents who died in the Holocaust than about those who were murdered at Stalin’s command.