<Li> Napoleon's Invasion of Russia </Li> <Li> Polish--Soviet </Li> <P> The Soviet invasion of Poland was a military operation by the Soviet Union without a formal declaration of war . On 17 September 1939, the Soviet Union invaded Poland from the east, sixteen days after 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 Germany and the Soviet Union . The joint German - Soviet invasion of Poland was secretly agreed to following the signing of the Molotov--Ribbentrop Pact on 23 August 1939 . </P> <P> The Red Army, which vastly outnumbered the Polish defenders, achieved its targets by using strategic and tactical deception . Some 230,000 Polish prisoners of war had been captured . The campaign of mass persecution in the newly acquired areas began immediately . In November 1939 the Soviet government ostensibly annexed the entire Polish territory under its control . Some 13.5 million Polish citizens who fell under the military occupation were made into new Soviet subjects following mock elections conducted by the NKVD secret police in the atmosphere of terror, the results of which were used to legitimize 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 . </P>

When did the soviet union take over poland