Soviet invasion of Poland

The Red Army’s 17 September 1939 invasion of eastern Poland, conducted under the secret protocol of the Molotov–Ribbentrop Pact while Poland was fighting Germany.

Molotov–Ribbentrop Pact: A 1939 nonaggression agreement between Nazi Germany and the Soviet Union, accompanied by a secret protocol dividing parts of Eastern Europe into spheres of influence. Its secret protocol assigned eastern Poland to the Soviet sphere before the Red Army crossed the border.
Soviet foreign policy under Joseph Stalin: The diplomacy and strategic choices of the Soviet Union under Joseph Stalin’s leadership. Stalin’s policy shifted from collective security toward an accommodation with Nazi Germany in 1939.
Katyń massacre: The 1940 execution by the Soviet secret police of thousands of Polish prisoners, including military officers and officials. Many victims had been captured after the Red Army’s invasion and occupation of eastern Poland.
German occupation of Poland: The Nazi German rule imposed on occupied Polish territories from 1939 to 1945. It differed from Soviet rule in administration and policy, though both followed the 1939 partition.
Secret Protocol to the Molotov–Ribbentrop Pact: A confidential 1939 agreement that defined German and Soviet spheres of influence in Eastern Europe. It specified the intended division of Polish territory underlying the invasion.
German invasion of Poland: The German attack on Poland beginning 1 September 1939, which began the Second World War in Europe. Germany’s campaign weakened Polish defenses before the Soviet Union attacked from the east.
Deportations from eastern Poland (1939–1941): The Soviet forced removals of hundreds of thousands of people from occupied eastern Poland to the interior of the USSR. These deportations transformed civilian life in the territory taken by the Red Army.
Soviet invasion of Finland: The Soviet Union’s attack on Finland in November 1939, which began the Winter War. It followed the invasion of Poland and likewise reflected Soviet efforts to secure strategic territory.
Soviet occupation of eastern Poland: The Soviet administration and control of eastern Polish territories from 1939 until the German invasion of the Soviet Union in 1941. It was the political and military outcome of the Red Army’s advance.
Interwar Poland: The Polish state established in 1918 and existing until its defeat and occupation in 1939. Its borders and multiethnic population shaped Soviet claims and territorial ambitions.

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