We are bizarrely one-tracked in our historical memory. Anything we dislike is compared to the Nazis. So, when Vladimir Putin actually invaded a neighbor, he was inevitably likened to Adolf Hitler. But we don’t have to look far to find an apter parallel. In September 1939, Stalin seized the eastern half of Poland. Unlike his Nazi allies, who simply absorbed the territory they wanted, Stalin made the conquered population vote in sham elections. Two congresses were established in eastern Poland — one supposedly representing ethnic Belarusians, the other ethnic Ukrainians. These two assemblies immediately petitioned to join, respectively, the Belarusian...