How the 1939 Invasion of Poland Started World War II

When many people, especially those in the U.S., think of WWII, the invasion of Poland isn’t their first thought. But it was actually what started the war.

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Destroyed building in Poland after the invasion

Hitler and his forces invaded Poland on September 1, 1939. War had been brewing for a few years before this, and Hitler had committed other aggressive acts before. But after he refused to get out of Poland, both Britain and France declared war on September 3, 1939. Read on to see how you can learn about World War II through historical facts in books.


Hitler first came to power in 1933 after he was appointed chancellor, and he ruled for approximately 12 years. He won elections by turning people’s humiliation and anger at losing their war onto Jewish people. He turned Germany into a war state with the intent on conquering all of Europe and getting rid of all Jewish people and other groups he deemed “inferior.” He spent years building up an army and spreading his corrupt manifesto across Germany. He spread hate and discrimination against groups of people such as Jews, Slavs, gay people, and more.

For more, you can read The Death of Democracy: Hitler’s Rise to Power and the Downfall of the Weimar Republic.

Policy of Appeasement

UK Prime Minister Neville Chamberlain holding up a piece of paper at a speech

World War I didn’t end until 1918, about 15 years before Hitler came to power. Europe was unprepared for another war, so even though several European countries were aware of what he was doing, they followed a policy of appeasement, especially Britain. This meant they would pacify Germany, an aggressive country, and negotiate in order to avoid war. Even as Germany started expanding and ignoring international boundaries that had existed since World War I, even as they actively sought to overturn the Treaty of Versailles, Britain and other European countries did nothing.

For more, you can read Appeasement: Chamberlain, Hitler, Churchill, and the Road to War.

Munich Agreement

Leaders Benito Mussolini, Adolf Hitler, and Neville Chamberlain during the Munich Agreement

This agreement took place on September 30, 1938, between Germany, Great Britain, Italy, and France. It allowed Germany to annex Sudetenland, which had been part of western Czechoslovakia since the end of World War I. Hitler had already absorbed Austria earlier that year, Hitler wanted Sudetenland because about three million Germans lived there, and he said they should be reunited in Germany. Hitler had threatened war if Sudetenland was not annexed. France, Britain, and Italy were not prepared for war, nor did they want it, so they agreed. Czechoslovakia, with no allies to help, was forced to submit and allow the occupation of German forces in Sudetenland.

For more, you can read Munich, 1938: Appeasement and World War II.

German-Soviet Non-Aggression Pact

Soviet Union Foreign Minister Vyacheslav Molotov signing Molotov-Ribbentrop Pact with German Minister of Foreign Affairs Joachim von Ribbentrop and Soviet Union Premier Joseph Stalin

Nazi Germany and the Soviet Union signed this pact in August 1939. Also called the Molotov-Ribbentrop Pact, it had two main purposes: it led to the joint invasion and occupation of Poland in September, and both countries (who were ideological enemies) promised not to attack each other for 10 years. This was a big part of what led to the war. This pact didn’t last long—in June 1941, Hitler tried to invade the Soviet Union. Operation Barbarossa initially succeeded, since the Soviet Union was unprepared, but the invasion ultimately failed by December of the same year.

For more, you can read Soviet-German Non-Aggression Pact 1939: In search of the historical truth

Invasion of Poland

After Sudetenland was annexed and occupied, Britain and France had promised Poland, Czechoslovakia’s neighbor, to protect their independence and freedom. This is why when Germany invaded Poland with over a million soldiers and a few thousand tanks and planes on September 1, 1939, France and Britain told Germany to get out. The policy of appeasement was no longer an option, and when Germany stayed, Britain and France declared war on September 3.

German troops invading Poland with jeeps

The justification for invading Poland was that Poland was going to invade Germany, which was untrue. The Soviet Union also invaded Poland on September 17, and worked with Germany to encircle Poland. With their combined military might, the Nazis and Soviet Union’s invasion succeeded when Warsaw surrendered on September 28. The last of Poland’s resistance surrendered in early October, though Poland never formally surrendered.

For more, you can read Poland 1939: The Outbreak of World War II.


Divided map of Poland after the invasion by Germany and Soviet Union

The invasion of Poland marked the beginning of the war, but Britain and France didn’t do much except declare war. After their victory, Germany and the Soviet Union divided Poland, getting western and eastern Poland respectively. Germany later divided its part into two: the Warthegau, which was annexed into Germany, and the General Government, which was treated like a colony, all under the name Third Reich. Those deemed “racially inferior” were forced to move to the General Government so that “ethnic Germans” were the only ones in Warthegau. Poland remained occupied until the end of the war.

For more, you can read Between Nazis and Soviets: Occupation Politics in Poland, 1939-1947.

War is horrible for everybody, and Poland was no exception. I can only hope that we all learn from past mistakes eventually.

For another article about WWII, click here.