The Soviet Invasion Eastern Poland (1939)

An often overlooked military campaign of WW2 is the 1939 Soviet invasion of Eastern Poland. It occurred as a result of the Molotov-Ribbentrop Pact, a non-aggression agreement between the Soviet Union and Nazi Germany. Following Germany's invasion of Poland, the Soviets exploited the agreement's secret protocol, marching into Poland's eastern territories on September 17. The Red Army swiftly occupied the region, meeting minimal resistance, as the bulk of the Polish Army was fighting against Germany. The Red Army did suffer several thousands of casualties.

The Soviet move effectively divided Poland between the two totalitarian powers. In the Soviet zone almost 200,000 people were arrested by the Soviet authorities of which 8,513 were executed. Later 22,000 members of the Polish military and intelligentsia were murdered by the NKVD on Stalin's orders, collectivily known as the Katyn Massacre. Many people were deported to Siberia and Kazakhstan and would not survive. In June 1941 Hitler broke the pact and invaded the USSR.