Nazi Germany’s assault on Poland opened the Second World War in Europe, beginning a campaign of invasion and occupation that would transform the continent and the lives of millions.
Before dawn on September 1, 1939, Nazi Germany launched an unprovoked invasion of Poland, attacking across multiple fronts with ground forces supported by armour and aircraft. In the Free City of Danzig, the German battleship Schleswig-Holstein opened fire on the Polish military transit depot at Westerplatte, creating one of the enduring images of the war’s opening hours.
The invasion marked the beginning of the Second World War in Europe. Britain and France, which had committed themselves to Poland’s defence, declared war on Germany two days later.
For Poland, however, September 1939 was not simply the opening chapter of a wider conflict. It was the beginning of years of occupation, mass killing, forced displacement and resistance. Germany attacked from the west, north and south; on September 17, the Soviet Union invaded eastern Poland. The country was ultimately divided between the two powers under arrangements rooted in the secret protocol of the German-Soviet Non-Aggression Pact signed days before the war.
Poland Under Attack
Adolf Hitler had already dismantled much of the post-First World War European order before turning against Poland. Germany remilitarized the Rhineland, annexed Austria in 1938 and then dismantled Czechoslovakia in stages.
On August 23, 1939, Germany and the Soviet Union signed the Molotov-Ribbentrop Pact. Publicly, it was a non-aggression agreement. A secret protocol divided parts of Eastern Europe into German and Soviet spheres of influence and contemplated a territorial and political rearrangement of Poland.
Germany attacked nine days later.
Nazi propaganda attempted to portray Germany as the victim. German operatives staged incidents, including an attack on the radio station at Gleiwitz, that were falsely attributed to Poland and used to support claims that German military action was retaliatory.
The scale of the actual invasion demonstrated extensive preparation.
German forces attacked from East Prussia and Germany to the north and west and, with Slovak participation, from the south. The Wehrmacht held major advantages in armour, aircraft, communications and the ability to concentrate mechanized forces against selected parts of the Polish defensive line.
Polish forces resisted across the country.
At Westerplatte, a small Polish garrison held out for seven days despite attacks from land, sea and air. Polish defenders also fought at the Polish Post Office in Danzig. At Mokra on September 1, the Wołyńska Cavalry Brigade resisted the German 4th Panzer Division, contradicting the enduring popular caricature that Polish cavalry simply charged German tanks with sabres.
As German forces advanced, civilians were caught directly in the campaign. Bombing, artillery fire and the movement of armies sent hundreds of thousands of Jewish and non-Jewish refugees onto roads leading eastward. Many carried little more than what they could take with them.
German armoured formations reached the outskirts of Warsaw within days, but the capital did not immediately fall. Polish troops and civilians defended the city under increasingly destructive bombardment.
The largest Polish counteroffensive came along the Bzura River beginning September 9. Polish forces initially gained ground and forced Germany to redirect troops, but German air and ground superiority eventually overwhelmed the offensive.
Then Poland was attacked from the other direction.
The Invasion of Poland Becomes a European War
On September 17, Soviet forces crossed Poland’s eastern frontier while Polish armies were still fighting Germany.
The Soviet intervention reflected the secret arrangements reached with Nazi Germany in August. Poland now faced two invading powers, making organized national defence increasingly untenable.
Warsaw surrendered on September 28 after sustained bombing and shelling. That same day, Germany and the Soviet Union signed a boundary and friendship treaty formalizing the division of occupied Polish territory. The last major organized Polish operational force surrendered in early October, although Polish resistance did not end.
The Polish government continued abroad, while Polish military personnel escaped through neighbouring countries and later fought alongside the Allies. Inside occupied Poland, an extensive underground state and resistance movement developed.
Britain and France had declared war on Germany on September 3 after Hitler failed to withdraw his forces. The invasion had therefore achieved something Hitler had hoped to avoid: transforming the attack on Poland into a broader European war.
The consequences for the Polish population were catastrophic.
German occupation policy was not limited to conventional military control. Nazi authorities targeted members of Poland’s political, intellectual, religious and cultural leadership, while Jews faced rapidly escalating persecution, dispossession, forced labour and confinement. Occupied Poland would later become the principal geographical setting for Nazi Germany’s extermination camps and much of the Holocaust.
Soviet rule in eastern Polish territories brought its own repression, including arrests, deportations and executions. In 1940, the Soviet NKVD murdered nearly 22,000 Polish prisoners and members of the Polish elite in the Katyn massacres and related executions.
Poland itself would not regain full sovereignty when the fighting ended in 1945. Its borders shifted westward, millions of people had been killed, communities were destroyed or displaced, and the country entered the Soviet sphere that dominated Eastern Europe for decades.
September 1, 1939, therefore represents more than the date traditionally used to mark the beginning of the Second World War in Europe. For Poland, it marked the destruction of the independent state between Nazi Germany and the Soviet Union and the beginning of nearly six years of devastating occupation and warfare.
The fighting at Westerplatte became a symbol of that experience: a small Polish position attacked in the first hours of a conflict that would eventually spread across continents.
What began in Poland that morning did not remain a Polish war. Within days, Europe’s major powers were again at war. Within years, the conflict had become global, leaving tens of millions dead and reshaping the international order.
About the Author Brad Socha is the founder of The Universal Record, focused on sourced, factual global reporting. Coverage includes international news, geopolitics, technology, and major developments.
