Germany Invades Poland, Starting World War II

Context

The Treaty of Versailles had left Germany resentful over territorial losses, including the Polish Corridor and the Free City of Danzig. After seizing power in 1933, Adolf Hitler pursued aggressive expansion, remilitarizing the Rhineland in 1936, annexing Austria in 1938, and dismantling Czechoslovakia through the Munich Agreement later that year. These moves emboldened him to press claims on Danzig and the corridor, while Poland refused to yield under its alliance guarantees from Britain and France.

What Happened

In the early hours of September 1, the German pre-dreadnought Schleswig-Holstein opened fire on the Polish military depot at Westerplatte near Danzig. Almost simultaneously, Luftwaffe aircraft struck targets across Poland, including the undefended town of Wieluń, and Wehrmacht units advanced from East Prussia in the north under Army Group North commanded by Fedor von Bock and from Silesia in the south under Army Group South led by Gerd von Rundstedt. Polish forces under Marshal Edward Rydz-Śmigły mounted counterattacks at places such as Mokra but faced overwhelming numerical and technological superiority in tanks and aircraft.

Aftermath

Britain and France issued ultimatums and declared war on Germany on September 3, though they provided no immediate military aid to Poland. Warsaw endured heavy bombardment and held out until its surrender on September 27. The Soviet Union invaded eastern Poland on September 17 in accordance with the secret protocols of the Molotov-Ribbentrop Pact, completing the partition of the country by early October.

Legacy

The campaign demonstrated the devastating speed of combined-arms blitzkrieg tactics and marked the start of a six-year global war that killed tens of millions. Poland's occupation became the site of the Holocaust's most systematic implementation, while the postwar settlement produced a divided Europe, the founding of the United Nations, and the emergence of Cold War blocs.