Germany Invades Poland and World War II Begins
The Nazi regime's war of conquest starts, and Europe's second continental war in a generation follows
Quick facts
- Invasion begins
- 1 September 1939
- Britain and France declare war
- 3 September 1939
- Soviet invasion of Poland
- 17 September 1939
- Secret agreement
- Molotov-Ribbentrop Pact
What happened
On 1 September 1939, Germany invaded Poland, prompting Britain and France to declare war two days later and beginning the Second World War in Europe. The invasion followed a rearmament program the Nazi regime had pursued since taking power in 1933 in direct violation of the Treaty of Versailles, along with a series of territorial moves, the remilitarization of the Rhineland, the annexation of Austria, and the dismemberment of Czechoslovakia, that Britain and France had failed to stop through a policy of appeasement. Poland was overwhelmed within weeks by combined German and, from 17 September, Soviet invasion under the terms of the secret Molotov-Ribbentrop Pact the two dictatorships had signed days before the war began.
Why it matters
This is the doorway into the war that would kill an estimated 70 to 85 million people worldwide and provide the cover under which the Holocaust was carried out. The full campaign history, the western and eastern fronts, the Holocaust's operational unfolding during the war, and Germany's eventual defeat and unconditional surrender in 1945 are covered in depth on this site's dedicated World War II timeline.
How we know
The invasion and its diplomatic run-up are documented through German and Allied government records, the text of the Molotov-Ribbentrop Pact's secret protocols (which surfaced after the war), and extensive contemporary press coverage.
Sources
- Holocaust Encyclopedia, United States Holocaust Memorial Museum. Nazi Rule · Reputable sourceencyclopedia.ushmm.org · The domain "encyclopedia.ushmm.org" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
- Holocaust Encyclopedia, United States Holocaust Memorial Museum. Timeline of Events · Reputable sourceencyclopedia.ushmm.org · The domain "encyclopedia.ushmm.org" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
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Related timelines
- World War II → · The complete World War II timeline, from the invasion of Poland through Germany's unconditional surrender in 1945