The Invasion of Poland in 1939 was a military offensive in which Nazi Germany, and two weeks later the Soviet Union, invaded Poland. It was the start of World War II in Europe. The invasion took place from 1 September to 6 October 1939. The invasion of Poland caused Britain and France to declare war on Germany on 3 September; they did little to affect the September Campaign. In the end, Poland lost. Germany and the Soviet Union divided the country according to a treaty signed years before the war.