On September 1, 1939, Germany invaded Poland after signing the Molotov-Ribbentrop Pact with the Soviet Union. The invasion by Germany and later by the Soviet Union lasted just over a month and ended with Germany and the Soviet Union dividing Poland. The invasion of Poland led Britain and France to declare war on Germany on September 3, 1941. This event started World War II in Europe.
An archival film summarizes Germany's preparations for war leading up to its invasion of Poland on September 1st, 1939. It proved to be the act of aggression that touched off World War II in Europe.