On September 1, 1939, the armed forces of Nazi Germany invaded Poland from the west initiating World War II. Two weeks later, on September 17, Soviet Union joined Germany in their attack on the Second Polish Republic. By early October, Poland was defeated. The occupied Poland was the only country in Europe where the Nazis had introduced a total ban on regional sports clubs. Football was allowed to be practised only by the Germans in the annexed areas of Upper Silesia. Polish activists and players risked their lives by organizing clandestine football competitions in Kraków, Warsaw and Poznań.