The Soviet Union invades Poland which was already in a state of war with Nazi Germany and occupies the Eastern part of Poland. At the end of September the division of Poland was confirmed by German–Soviet Treaty of Friendship, Cooperation and Demarcation.
The treaty included a correction of the borders first drawn in the secret clause of the Ribbentrop-Molotov Pact. It was the beginning of a 2-year long occupation of Central Europe by two totalitarian regimes. More