The start of World War II was triggered by Adolf Hitler's invasion of Poland on September 1, 1939. This invasion followed the signing of the German-Soviet Nonaggression Pact, which allowed Hitler to attack Poland without fear of a two-front war, as it included provisions for dividing Poland between Germany and the Soviet Union [1][4]. The subsequent declarations of war by Britain and France against Germany on September 3, 1939, marked the official beginning of the conflict [3][4].

What triggered the start of World War II?

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