Map from "Pinsk under Soviet Occupation" blog.

Americans with any feel for 20th century history may be reliably expected to know the significance of the date September 1, 1939 -- the day the Nazis started World War II from the West by invading Poland.

September 17, 1939, however, is the date that the the Soviets, our "premature allies," started World War II from the East by invading Poland. That's another story altogether. This date is not well known. Nor, really, is the Soviet rampage through Poland -- or even, much, the period of Nazi-Soviet alliance (1939-1941) in which Hitler and Stalin secretly divided up Europe. This same heinous division, by the way, was ultimately observed, sans Nazis, by Churchill and FDR and utlimately would set the battle lines of the Cold War.  

To be sure, it all made a moral hash out of the Nuremberg Trials, where the Nazis were tried and convicted for the crime against humanity of making aggressive war, while their equally aggressive and guilty war-making henchmen, the Soviets, were not even charged -- and, indeed, sat on the bench meting out "justice."

And we call Nuremberg perfect, lodestar Justice of the ages....

You can read why in American Betrayal.