The Russian Invasion of Poland, September 17, 1939
In early 1939, several months before the invasion, the Soviet Union began strategic alliance negotiations with the United Kingdom and France against the crash militarization of Nazi Germany under Adolf Hitler.
Joseph Stalin pursued the Molotov–Ribbentrop Pact with Adolf Hitler, which was signed on August 23, 1939. This non-aggression pact contained a secret protocol, that drew up the division of Northern and Eastern Europe into German and Soviet spheres of influence in the event of war.
On September 1, 1939, one week after the signing of the Molotov–Ribbentrop Pact, German forces invaded Poland from the west, north, and south. Polish forces gradually withdrew to the southeast where they prepared for a long defense of the Romanian Bridgehead and awaited the French and British support and relief that they were expecting. Neither the French nor the British came to Poland’s rescue.
On September 17, 1939 the Soviet Red Army invaded Poland from the east, in accordance with the secret protocol.
At the opening of hostilities, several Polish cities including Dubno, Łuck, and Włodzimierz Wołyński let the Red Army in peacefully, convinced that the Russians were on their way to defending Poland from the Germans. General Juliusz Rómmel of the Polish Army issued an unauthorised order to treat the Russians like an ally.
The Soviet government announced it was acting to protect the Ukrainians and Belarusians who lived in the eastern part of Poland, because the Polish state had collapsed.
Soviet propaganda portrayed the idea to the Polish people that Germany’s overwhelming “blitzkrieg” (“lightning war”) attack against Poland required the intervention of Soviet aid to protect Poland from the Germans.
One day after this unexpected second attack by the Russians from the east, the Polish government concluded that the defense of Poland was no longer feasible, and ordered the emergency evacuation of Polish troops to then-neutral Romania.
Sixteen days after Nazi Germany invaded Poland from the west, north, and south, the Soviet Union invaded Poland in a surprise attack from the east, without a formal declaration of war, on September 17, 1939.
Nazi German and Soviet Russian military operations lasted for the following 20 days, ending on October 6, 1939 with the two-way division and annexation of the entire territory of the Second Polish Republic by Nazi Germany and the Soviet Union.
The Soviet and Nazi collusion to invade Poland was specified in the “secret protocol” of the Molotov–Ribbentrop Pact signed by Nazi Germany and the Soviet Union on August 23, 1939, which divided Poland into Nazi and Soviet “spheres of influence.”
The Red Army vastly outnumbered the Polish defenders, encountering only limited resistance. Some 320,000 Poles were made prisoners of war. The Soviets and Nazis initiated immediate campaigns of mass persecution in their newly acquired spheres of influence. In November 1939, the Nazi and Soviet governments annexed the entirty of Poland under their control.
Some 13.5 million Polish citizens who fell under the military occupation were made Soviet subjects following show elections conducted by the NKVD secret police in an atmosphere of terror, the results of which were used to legitimise the use of force.
A Soviet campaign of political murders and other forms of repression, targeted Polish authority figures, including military officers, police, and priests, began with a wave of arrests and summary executions. The Soviet NKVD sent hundreds of thousands of people from eastern Poland to Siberia and other remote parts of the Soviet Union in four major waves of deportation between 1939 and 1941.
Soviet forces occupied eastern Poland until the summer of 1941 when Germany terminated its earlier pact with the Soviet Union and invaded the Soviet Union on June 22, 1941 in Operation Barbarossa.
All of Poland remained under German occupation until the Red Army reconquered Poland in the summer of 1944.
An agreement at the Yalta Conference permitted the Soviet Union to annex territories close to the Curzon Line (which almost coincided with all of their Molotov–Ribbentrop Pact portion of the Second Polish Republic), compensating the Polish People’s Republic with the greater southern part of East Prussia and territories east of the Oder–Neisse line. The Soviet Union appended the annexed territories to the Ukrainian, Byelorussian and Lithuanian Soviet Socialist Republics.
Following the end of World War II in Europe, the Soviet Union signed the Polish–Soviet border agreement of August 1945 with the new, internationally recognized Polish Provisional Government of National Unity on August 16, 1945. This agreement recognized the status quo as the new official border between the Soviet Union and Poland, with the exception of the region around Białystok and a minor part of Galicia east of the San River around Przemyśl, which were later returned to Poland.