With the largest number of ethnic Germans living in Russia, Hitler knew that he could not resettle all these people without the full cooperation of Joseph Stalin and the Soviet Union. In late August 1939 (a week before the invasion of Poland and the start of World War II in Europe), Hitler sent his foreign minister Joachim von Ribbentrop to Moscow to arrange a pact of non aggression with the Soviet Union. This became known as the Molotov–Ribbentrop Pact.