Invaded Poland in the context of "Plan West"

The Soviet invasion of Poland was a military conflict by the Soviet Union without a formal declaration of war. On 17 September 1939, the Soviet Union invaded Poland from the east, 16 days after Nazi Germany invaded Poland from the west. Subsequent military operations lasted for the following 20 days and ended on 6 October 1939 with the two-way division and annexation of the entire territory of the Second Polish Republic by Nazi Germany and the Soviet Union. This division is sometimes called the Fourth Partition of Poland. The Soviet (as well as German) invasion of Poland was indirectly indicated in the "secret protocol" of the Molotov–Ribbentrop Pact signed on 23 August 1939, which divided Poland into "spheres of influence" of the two powers. German and Soviet cooperation in the invasion of Poland has been described as co-belligerence.

The Red Army, which vastly outnumbered the Polish defenders, achieved its targets, encountering only limited resistance. Some 320,000 Poles were made prisoners of war. The campaign of mass persecution in the newly acquired areas began immediately. In November 1939 the Soviet government annexed the entire Polish territory under its 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, targeting Polish figures of authority such as 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 under the code name Operation Barbarossa. The area was under German occupation until the Red Army reconquered it 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.

The Holocaust saw the ghettoization, robbery, deportation and mass murder of Jews, alongside other groups under similar racial pretexts in occupied Poland by the Nazi Germany. Over three million Polish Jews were murdered, primarily at the Chełmno, Belzec, Sobibor, Treblinka and Auschwitz extermination camps, who made up half of the Jewish Holocaust victims.

During Nazi occupation, the country lost 20% of its population, or six million people, including three million Jews (90% of the country's Jewish population). All Poles, Christian or Jewish, were bound for total annihilation. In 1939, Nazi Germany invaded Poland while the Soviet Union invaded Poland from the east. In German-occupied Poland, Jews were killed, subjected to forced labor, and forced to move to ghettos. Some 7,000 Jews were killed in 1939, but open mass killings subsided until June of 1941. The Soviet Union deported many Jews to the Soviet interior, where most survived the war. In 1941, Germany invaded the Soviet Union and began the systematic murder of Jews. 1.8 million Jews were killed in Operation Reinhard, shot in roundups in ghettos, died during the train journey, or killed by poison gas in the extermination camps. In 1943 and 1944, the remaining labor camps and ghettos were liquidated. Many Jews tried to escape, but surviving in hiding was very difficult due to factors such as the lack of money to pay helpers and the risk of denunciation. Only 1 to 2 percent of Polish Jews in German-occupied territory survived. After the war, survivors faced difficulties in regaining their property and rebuilding their lives. Especially after the Kielce pogrom, many fled to displaced persons camps in Allied-occupied Germany.

The Holocaust saw the ghettoization, robbery, deportation and mass murder of Jews in occupied Poland by Nazi Germany. Over three million Polish Jews were murdered, primarily at the Chełmno, Belzec, Sobibor, Treblinka and Auschwitz extermination camps, who made up half of the Jewish Holocaust victims.

During Nazi occupation, the country lost 20% of its population, or six million people, including three million Jews (90% of the country's Jewish population). In 1939, Nazi Germany invaded Poland while the Soviet Union invaded Poland from the east. In German-occupied Poland, Jews were killed, subjected to forced labor, and forced to move to ghettos. Some 7,000 Jews were killed in 1939, but open mass killings subsided until June of 1941. The Soviet Union deported many Jews to the Soviet interior, where most survived the war. In 1941, Germany invaded the Soviet Union and began the systematic murder of Jews. 1.8 million Jews were killed in Operation Reinhard, shot in roundups in ghettos, died during the train journey, or killed by poison gas in the extermination camps. In 1943 and 1944, the remaining labor camps and ghettos were liquidated. Many Jews tried to escape, but surviving in hiding was very difficult due to factors such as the lack of money to pay helpers and the risk of denunciation. Only 1 to 2 percent of Polish Jews in German-occupied territory survived. After the war, survivors faced difficulties in regaining their property and rebuilding their lives. Especially after the Kielce pogrom, many fled to displaced persons camps in Allied-occupied Germany.