Drang nach Osten
Even though Japan had been invading in China since 1937, the conventional view is that the war began on September 1, 1939, when Nazi Germany invaded Poland, the Drang nach Osten. Within two days the United Kingdom and France declared war on Germany, even though the fighting was confined to Poland. Pursuant to a then-secret provision of its non-aggression Molotov–Ribbentrop Pact, the Soviet Union joined with Germany on September 17, 1939, to conquer Poland and to divide Eastern Europe.