context: The Soviet invasion of Poland is a Soviet military operation that began without an official announcement on September 17, 1939. That morning, 16 days after Nazi Germany invaded Poland from the west, the Soviet Union invaded Poland from the east. The invasion and battle continued for 20 consecutive days and ended on October 6, 1939 with the annexation of the entire territory of the Second Polish Republic by both Germany and the Soviet Union. [1] The German-Soviet invasion of Poland was secretly agreed upon in the Molotov-Ribbentrop Agreement signed on August 23, 1939. [2]
question: When did the Soviet invasion of Poland begin?
answers.text: September 17, 1939