Soviet invasion of Poland was a Soviet military operation that started without a formal declaration of war on 17 September 1939, during the early stages of WWII. 16 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 2nd Polish Republic by Germany and The USSR.
World War 2 This war fought in Europe, North Africa and Asia started in 1939 with the invasion of Poland by Nazi Germany and ended in 1945 with the dropping of two atomic bombs on Japan. It was the largest armed conflict in history.