Completed the following sentence: On September 1, 1939, Nazi Germany invaded Poland and started World War II. ️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️ <unk> <unk> <unk> <unk>
️<unk>️<unk>️<unk>️<unk>️<unk>️ ️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️<unk>️ Finland lost its natural border along the Rajajoki River () in the south. Finland lost its natural border along the Rajajoki River () in the south. 22,973 km2, or 71.5 percent of the province on the Karelian Isthmus, including the cities of Viipuri and Sortavala, became part of the newly established Karelo-Finnish SSR in the Soviet Union. ️<unk>️<unk>️<unk>️<unk>