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How did Adolf Hitler’s invasion of Poland begin World War II?

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Portrait of Adolf Hitler in a collared shirt and tie, facing forward with a serious expression, circa 1933. — Adolf Hitler Nazi Party leader Adolf Hitler, c. 1933.

Adolf Hitler’s invasion of Poland triggered World War II by violating the sovereignty of a nation that had received military guarantees from Great Britain and France.12

To ensure the invasion could proceed without interference, Hitler secured the German-Soviet Nonaggression Pact in August 1939, which included a secret protocol to partition Poland between Nazi Germany and the Soviet Union. Believing this agreement neutralized the threat of a two-front war, Hitler ordered the invasion to commence on September 1, 1939.13

The German military employed blitzkrieg tactics, launching a massive, coordinated assault across the border. Because Britain and France had pledged to defend Poland, they issued ultimatums to Germany and subsequently declared war on September 3, 1939, marking the official beginning of the global conflict.421