Soviet invasion of Poland
The Peace of Riga treaty signed on the 18th of March 1921 drew a new line between Poland and Soviet Russia. This agreement divided disputed territories after the Polish-Soviet War of 1920 ended with an armistice in October that year. Józef Piłsudski had sought to expand Polish borders as far east as possible to create a federation capable of countering imperialist action from Russia or Germany. The Red Army, commanded by Trotsky and Stalin among others, advanced deep into Ukraine and Belarus before the joint Polish-Ukrainian armies captured Kyiv. A massive counteroffensive by the Red Army culminated in the Battle of Warsaw where the Soviets sued for peace. The Conference of Ambassadors recognized Poland's eastern frontiers in 1923 except for Lithuania. Soviet leaders steadily abandoned the idea of international Communist revolution following this peace agreement.
German Foreign Minister Joachim von Ribbentrop handed British Ambassador Nevile Henderson a list of terms on the 29th of August 1939 regarding Poland. On the 24th of August 1939 the Soviet Union and Germany signed the political and military arrangements known as the Molotov-Ribnertrop Pact. This pact contained secret protocols regulating detailed plans for the division of states in northern and eastern Europe into German and Soviet spheres of influence. The Soviet sphere initially included Latvia Estonia and Finland while Germany and the Soviet Union would partition Poland. Territories east of the Pisa Narev Vistula and San rivers fell to the Soviet Union. Joseph Stalin pursued this non-aggression pact with Adolf Hitler after months of strategic alliance negotiations with Britain and France against Nazi militarization.
On the 17th of September 1939 the Red Army crossed the border into Poland from the east. Marshal Semyon Timoshenko commanded the invasion on the Ukrainian Front while General Mikhail Kovalyov led forces on the Belarusian Front. A Red Army force of seven field armies entered eastern Poland with combined strength between 450,000 and 1,000,000 troops. Polish sources give a number of over 800,000. By the 28th of September the Red Army reached the Narew Western Bug Vistula and San rivers line agreed upon in advance with Germany. The last operational unit of the Polish Army was General Franciszek Kleeberg's Independent Operational Group Polesie which surrendered on the 6th of October after the four-day Battle of Kock. Molotov reported to the Supreme Soviet on the 31st of October that a short blow by the German army followed by the Red Army left nothing of the state created at the Treaty of Versailles.
German General Heinz Guderian and Soviet Brigadier Semyon Krivoshein held a joint parade in the town of Lwów on the 22nd of September. Wehrmacht troops passed the Brest Fortress to the Soviet 29th Tank Brigade on the 17th of September following the Battle of Brześć Litewski. Soviet units met their German counterparts during advancement from opposite directions. Notable occurrences of cooperation in the field among the two armies were reported as they advanced across Poland. On the 24th of September 1939 the Soviet Union and Germany signed the German-Soviet Treaty of Friendship Cooperation and Demarcation readdressing secret terms of the earlier pact. Lithuania was incorporated into the Soviet sphere of influence while the border within Poland shifted east increasing German territory. This arrangement often described as a fourth partition of Poland secured almost all Polish territory east of the river line for the Soviet Union.
The NKVD killed 22,000 Polish military personnel and civilians in the Katyn massacre in 1940. Torture was widely used by the NKVD in various prisons especially in small towns. During the two years following annexation the Soviet police forces arrested approximately 100,000 Polish citizens. The Soviet government confiscated nationalized and redistributed all private Polish property. In four major waves between 1939 and 1941 hundreds of thousands of people from eastern Poland were sent to Siberia and other remote parts of the Soviet Union. Estimates on the number of people deported to Siberia and those who perished under Soviet wartime rule amounted to around 150,000 Polish citizens according to research announced in August 2009. The Soviet authorities suppressed anti-Polish movements including the Organization of Ukrainian Nationalists which had actively resisted Polish regime since the 1920s.
Britain and France refrained from critical reaction to the Soviet invasion and annexation of Eastern Poland since neither expected confrontation with the Soviet Union at that time. British Prime Minister Neville Chamberlain considered making a public commitment to restore the Polish state but eventually issued only general condemnations. Public opinion in Britain varied among expressions of outrage at the invasion and perception that Soviet claims in the region were reasonable. While France had made promises to Poland including provision of air support these were not honored. French forces advanced tentatively into the Saar region in early September but retreated behind the Maginot Line upon Polish defeat on the 4th of October. Winston Churchill stated in public on the 1st of October 1939 that modern scholarship has described German and Soviet cooperation as co-belligerence since the Molotov-Ribbentrop Pact was not an official alliance.
The Soviet Union signed the Polish-Soviet border agreement of August 1945 with new internationally recognized Polish Provisional Government of National Unity on the 16th of August 1945. This agreement recognized status quo as new official border between two countries except for region around Białystok and minor part of Galicia east of San River around Przemyśl later returned to Poland. An agreement at Yalta Conference permitted Soviet Union to annex territories close to Curzon Line which almost coincided with all their Molotov-Ribnertrop Pact portion of Second Polish Republic. The Red Army reconquered area under German occupation in summer of 1944 after Germany terminated earlier pact and invaded Soviet Union under Operation Barbarossa in summer of 1941. The Soviet Union appended annexed territories to Ukrainian Byelorussian and Lithuanian Soviet Socialist Republics.
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Common questions
When did the Soviet Union invade Poland in 1939?
The Red Army crossed the border into Poland on the 17th of September 1939. Marshal Semyon Timoshenko commanded the invasion on the Ukrainian Front while General Mikhail Kovalyov led forces on the Belarusian Front.
What was the purpose of the Molotov-Ribbentrop Pact signed on the 24th of August 1939?
The pact contained secret protocols regulating detailed plans for the division of states in northern and eastern Europe into German and Soviet spheres of influence. The agreement allowed Germany and the Soviet Union to partition Poland with territories east of the Pisa Narev Vistula and San rivers falling to the Soviet Union.
How many Polish citizens were killed or deported during the Soviet occupation between 1939 and 1941?
Research announced in August 2009 estimates that around 150,000 Polish citizens perished under Soviet wartime rule or were sent to Siberia and other remote parts of the Soviet Union. The NKVD killed 22,000 Polish military personnel and civilians in the Katyn massacre in 1940 alone.
Which countries refrained from critical reaction to the Soviet invasion of Eastern Poland in September 1939?
Britain and France refrained from critical reaction to the Soviet invasion and annexation of Eastern Poland since neither expected confrontation with the Soviet Union at that time. French forces advanced tentatively into the Saar region in early September but retreated behind the Maginot Line upon Polish defeat on the 4th of October.
When did the Soviet Union sign the final border agreement with Poland after World War II?
The Soviet Union signed the Polish-Soviet border agreement of August 1945 with new internationally recognized Polish Provisional Government of National Unity on the 16th of August 1945. This agreement recognized status quo as new official border between two countries except for region around Białystok and minor part of Galicia east of San River around Przemyśl later returned to Poland.