Soviet invasion of Poland

The 1939 Soviet invasion of Poland was a Soviet military operation that started without a formal declaration of war on 17 September 1939, immediately after the undeclared war between the Soviet Union and the Empire of Japan at the Battles of Khalkhin Gol (Nomonhan) in the Far East. The Molotov-Togo agreement between the USSR and Japan was signed on 15 September 1939, with a cease fire taking effect on 16 September 1939.[6] On 17 September, sixteen days after Nazi Germany invaded Poland from the west, the Soviet Union did so from the east. The invasion ended on 6 October 1939 with the division and annexing of the whole of the Second Polish Republic by Germany and the Soviet Union.[7] In early 1939, the Soviet Union entered into negotiations with the United Kingdom, France, Poland, and Romania to establish an alliance against Nazi Germany. The negotiations failed when the Soviet Union insisted that Poland and Romania give Soviet troops transit rights through their territory as part of a collective security agreement.[8] The failure of those negotiations led the Soviet Union to conclude the Molotov-Ribbentrop Pact with Nazi Germany on 23 August; this was a non-aggression pact containing a secret protocol dividing Northern and Eastern Europe into German and Soviet spheres of influence.[9] One week after the signing of the Molotov-Ribbentrop Pact, German forces invaded Poland from the north, south, and west. Polish forces then withdrew to the southeast where they prepared for a long defence of the Romanian Bridgehead and awaited the French and British support and relief that they were expecting. The Soviet Red Army invaded the Kresy, in accordance with the secret protocol, on 17 September.[10][Note 5] 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 in the face of the Nazi German attack and could no longer guarantee the security of its own citizens.[13][14][15][16

Facing a second front, the Polish government concluded that the defence of the Romanian Bridgehead was no longer feasible and ordered an emergency evacuation of all troops to neutral Romania.[1] The Red Army achieved its targets, vastly outnumbering Polish resistance and capturing some 230,000 Polish prisoners of war.[4][17] The Soviet government annexed the territory under its control and in November 1939 made the 13.5 million formerly Polish citizens now under its control citizens of the Soviet Union. The Soviet Union immediately started a campaign of sovietizing the newly acquired areas. This included staged elections, the results of which the Soviet Union used to legitimize its annexation of eastern Poland. The Soviets quelled opposition through summary executions and thousands of arrests.[18][19] The Soviet Union sent hundreds of thousands of people from this region to Siberia and other remote parts of the Soviet Union in four major waves of deportation between 1939 and 1941.[Note 6] Soviet forces occupied eastern Poland until the summer of 1941, when they were expelled by the invading German army in the course of Operation Barbarossa. The area was under Nazi occupation until the Red Army reconquered it in the summer of 1944. An agreement at the Yalta Conference permitted the Soviet Union to annex almost all of their Molotov-Ribbentrop Pact portion of the Second Polish Republic, compensating the People's Republic of Poland with the southern half of East Prussia and territories east of the Oder-Neisse Line.[22] The Soviet Union folded most of the annexed territories into the Ukrainian Soviet Socialist Republic and the Byelorussian Soviet Socialist Republic.[22] In August 1945, after the end of World War II in Europe, USSR and Poland signed a border agreement. This agreement recognized the status quo as the official border with the exception of the region around Bialystok and a minor part of Galicia east of the San river around Przemysl, which where returned to Poland.