Battles & Wars › World War II › World War II
German invasion of Poland
September 1 – October 6, 1939· Battle· Europe
Well documentedSolid records, physical evidence or scientific consensus.
Germany attacked Poland on September 1, 1939; the Soviet Union invaded from the east on September 17, and the two partitioned the country.
See it on the Battles & Wars map →What happened
Using a staged 'Polish' attack on a German radio station at Gleiwitz as a pretext, about 1.5 million German troops struck from three sides. Polish forces fought hard but were outnumbered, outgunned and outflanked. Under a secret protocol of the Nazi–Soviet Pact, the Red Army then occupied eastern Poland. Warsaw surrendered on September 28 after heavy bombing, and the last Polish units on October 6. Britain and France declared war but sent no real help.
Why it matters
It started World War II in Europe and began an occupation in which roughly one in six Polish citizens died, including about 3 million Polish Jews.
How we know
German and Polish military records, Nuremberg testimony on the Gleiwitz incident, and the Nazi–Soviet Pact's secret protocol, published after the war and admitted by Moscow only in 1989.
Still debated
Casualty figures vary; historians also debate whether a French offensive against Germany's thinly held western border in September 1939 could have changed the outcome.
Connections (3)
▸German invasion of Poland started World War IIWell documented
The connection
Britain and France had guaranteed Poland's independence in March 1939. When Germany invaded on September 1 and ignored their ultimatums, both declared war on September 3, turning a German–Polish war into a European one that later drew in the Soviet Union, Japan and the United States.
When and how
Poland, September 1, 1939; British and French declarations of war on September 3, followed within days by Australia, New Zealand, India, South Africa and Canada.
How we know
The declarations of war and diplomatic records are unambiguous; September 1, 1939 is the standard start date in Western histories.
Debates and open questions
Some historians date the war's start to Japan's 1937 invasion of China, or treat December 1941 as the moment it became truly global.
▸Blitzkrieg (combined-arms maneuver warfare) was first seen in German invasion of PolandMostly agreed
The connection
In Poland, German panzer and motorized divisions, backed by dive-bombers, broke through and encircled Polish armies within weeks. The speed led Western journalists to popularize the word 'Blitzkrieg'. Yet much of the campaign was a conventional infantry advance with horse-drawn supply, and the Soviet invasion from the east sealed Poland's fate.
When and how
Poland, September 1939; Guderian's panzer corps cut across the Polish Corridor and then drove south toward Brest.
How sure are we?
German campaign records and the Western press of September 1939, including Time magazine's early use of 'Blitzkrieg', document both the methods and the label.
Debates and open questions
Many historians argue Poland was not yet true blitzkrieg; the method fully emerged in France in 1940, when tanks were massed decisively at one point.
▸Enigma machine had already been broken by Poles before the German invasion of PolandWell documented
The connection
Poland's Cipher Bureau read German Enigma messages for much of the 1930s, until new German procedures in late 1938 swamped its methods. On July 25–26, 1939, five weeks before the invasion, the Poles handed French and British codebreakers their methods and two replica Enigmas. After Poland fell, its codebreakers escaped to France and kept working.
When and how
Pyry forest near Warsaw, July 25–26, 1939; Marian Rejewski, Jerzy Różycki and Henryk Zygalski; Gustave Bertrand of France; Alastair Denniston and Dilly Knox of Britain.
How we know
Rejewski's and Bertrand's accounts, British records of the meeting, and Bletchley Park histories crediting the Polish start.
Debates and open questions
How many months the Polish gift saved Bletchley is debated, but most historians call it crucial.