Germany Invades Poland in 1939 The Start of World War II
At dawn on 1 September 1939, German forces crossed into Poland by land, sea, and air. Within hours, bombs fell on Polish towns, troops pushed across the border, and Europe moved towards a war that would become global.
The invasion did not come from nowhere. It followed years of aggressive expansion by Nazi Germany, failed diplomacy, and secret deals between dictatorships. It also exposed the limits of appeasement, the weakness of international safeguards, and the danger of treating smaller states as bargaining pieces.
When Germany invaded Poland in 1939, Britain and France faced a clear test. They had promised to defend Polish independence. On 3 September, after Germany ignored demands to withdraw, both declared war. That moment marked the beginning of the Second World War in Europe.
Europe was already under severe strain before 1939
The attack on Poland came after a long breakdown in European order.
After the First World War, the Treaty of Versailles reshaped borders and placed limits on Germany’s military. Many Germans resented the settlement, and Adolf Hitler used that resentment to gain support. He promised to rebuild German power, overturn Versailles, and create living space in Eastern Europe.
By the late 1930s, Nazi Germany had already taken major steps towards war:
Germany remilitarised the Rhineland in 1936.
Austria was annexed in 1938.
The Sudetenland, a border region of Czechoslovakia, was handed to Germany after the Munich Agreement in September 1938.
In March 1939, German troops occupied the rest of Czech lands.
Each move weakened trust in diplomacy. Britain and France had hoped concessions might prevent a wider conflict. Instead, Hitler read hesitation as weakness.
Poland was next in his sights for several reasons. Germany wanted the Free City of Danzig, now Gdańsk, and sought control over the Polish Corridor, which gave Poland access to the Baltic Sea and separated East Prussia from the rest of Germany. Nazi ideology also treated Poland not as a neighbour with rights, but as territory to dominate.
Poland understood the danger. It refused German demands that would have undermined its sovereignty. In March 1939, Britain gave a guarantee to support Poland if its independence came under threat. France had its own alliance commitments to Poland.
The crisis became even more dangerous in August 1939. Germany and the Soviet Union signed the Nazi-Soviet Pact, also known as the Molotov-Ribbentrop Pact. Publicly, it was a non-aggression agreement. Secretly, it divided much of Eastern Europe into German and Soviet spheres of influence. Poland stood between them.
That pact gave Hitler confidence that Germany could attack Poland without immediately facing the Soviet Union as an enemy. It also sealed Poland’s fate from both sides.
The invasion began with speed and force
Germany attacked Poland in the early hours of 1 September 1939. The assault came from several directions at once. German forces advanced from the west, north, and south. Troops moved from Germany, East Prussia, and German-controlled territory in Slovakia.
The German battleship Schleswig-Holstein fired on the Polish military depot at Westerplatte near Danzig. German aircraft struck airfields, railways, roads, communication lines, and towns. The aim was to cause shock, break Polish command, and prevent effective movement of reinforcements.
The German strategy relied on close coordination between tanks, infantry, aircraft, and radio communication. Later, people often used the term Blitzkrieg, or lightning war, to describe this method. The word can make the campaign sound neat and unstoppable, but the reality was brutal, chaotic, and deeply destructive.
Polish forces resisted fiercely. They were not passive victims of a sudden collapse. Poland fought under severe disadvantages:
Germany had larger and better-equipped forces.
Poland faced attack from multiple directions.
German air power disrupted movement and supply.
Poland’s allies did not launch a major immediate offensive in the west.
Poland’s military plan expected to defend key areas long enough for Britain and France to increase pressure on Germany. That relief did not come in time.
German propaganda also played a role. Nazi leaders staged or exaggerated border incidents to claim Germany was acting in self-defence. The most notorious was the Gleiwitz incident, used as part of the pretext for war. These claims did not reflect the reality of German planning. The invasion was prepared in advance and formed part of a wider programme of conquest.
Britain and France declared war after Germany refused to withdraw
Britain and France had promised to support Poland. After the invasion began, they sent Germany demands to stop the attack and withdraw its forces. Germany did not comply.
On 3 September 1939, Britain declared war on Germany. France followed the same day.
This is why the invasion of Poland is usually treated as the start of the Second World War in Europe. Earlier conflicts mattered, including Japan’s war in China from 1937 and Italy’s aggression in Africa. Yet in Europe, 3 September turned a German-Polish war into a wider war involving major powers.
The declarations did not save Poland in the short term. Britain and France were not ready to strike Germany with enough force to change the campaign. There was limited action in the west, but no major offensive that pulled German pressure away from Poland.
For many Poles, this became a bitter memory. Their country had stood against Nazi demands, yet the promised help did not arrive in a form that could stop defeat.
Germany’s attack also showed how quickly modern war could target more than armies. Air raids and artillery hit infrastructure and civilian areas. Roads filled with refugees. Families fled eastward, often without clear information about where safety might be found.
The war was not only a clash of states. It became a catastrophe for civilians almost from the first day.
The Soviet invasion broke Poland from the east
On 17 September 1939, the Soviet Union invaded Poland from the east. Soviet leaders claimed they were protecting people in eastern Poland after the Polish state had supposedly collapsed. In reality, the invasion followed the secret terms of the Nazi-Soviet Pact.
This second invasion made Poland’s military position almost impossible. Polish forces had already been fighting Germany for more than two weeks. Now they faced another powerful army from the opposite direction.
The Soviet entry changed the campaign in three major ways.
First, it cut off options for organised retreat. Polish leaders had hoped some forces might fall back towards the south-east, near the Romanian and Hungarian borders, and continue resistance. Soviet forces severely reduced that possibility.
Second, it confirmed that Poland had been partitioned by two hostile powers. Germany and the Soviet Union later formalised their division of occupied Poland.
Third, it began a separate period of Soviet repression in eastern Poland. Deportations, arrests, and executions followed. Polish officers, officials, teachers, police, and other members of society were targeted. German occupation in the west and Soviet occupation in the east differed in ideology and method, but both involved violence, control, and the crushing of Polish independence.
Poland’s government crossed into exile, first through Romania. It did not surrender. Polish armed forces continued to fight alongside the Allies in several theatres of the war, including in the air, at sea, in North Africa, in Italy, and in Western Europe.
That matters because the fall of Poland did not mean the end of Polish resistance. It meant the start of a long occupation and a long struggle from inside and outside the country.
Warsaw held out under heavy attack
Warsaw, Poland’s capital, became a symbol of resistance. German forces surrounded and bombarded the city. Civilians and soldiers endured air raids, shelling, shortages, fire, and the collapse of basic services.
The city surrendered on 28 September 1939 after intense destruction and loss of life. The decision came when continued defence could no longer change the military outcome and would only bring more suffering to the population.
Other Polish forces continued fighting after Warsaw’s surrender. The final major battle of the campaign, the Battle of Kock, ended on 6 October 1939. By then, organised resistance inside Poland had been defeated, though underground resistance soon developed.
The German victory was fast, but it was not effortless. Polish units fought hard in many places, including Westerplatte, the Bzura River, the defence of Warsaw, and other local battles. The speed of German success came from strategic advantage, powerful coordination, and Poland’s isolation, not from a lack of Polish courage.
The occupation that followed was among the harshest in Europe. Nazi Germany aimed to destroy Polish political and cultural life. It arrested and murdered members of the educated classes, forced labour on civilians, and treated Poles as inferior under racist ideology.
For Jewish people in Poland, the consequences became even more catastrophic. Poland had one of the largest Jewish populations in Europe before the war. German occupation led to ghettos, mass shootings, deportations, and extermination camps. The Holocaust cannot be separated from the occupation that began in 1939.
The invasion, then, was not only a military event. It opened the door to years of terror, genocide, forced labour, displacement, and resistance.
The attack on Poland changed the world
The invasion of Poland marked a turning point because it ended any remaining belief that Hitler’s ambitions could be contained through concessions.
Before September 1939, some leaders in Britain and France hoped Germany might stop after revising certain borders. Poland proved that Nazi expansion had no limited end point. The German state had prepared for conquest, occupation, and racial domination in the east.
The war that began in Europe soon widened. Germany attacked Denmark and Norway in 1940, then the Netherlands, Belgium, Luxembourg, and France. Britain fought on. In 1941, Germany invaded the Soviet Union. The same year, Japan attacked Pearl Harbour, and the United States entered the war. A regional European crisis had become part of a global conflict.
Poland’s fate also shaped post-war politics. At the end of the Second World War, Poland was liberated from Nazi rule but fell under Soviet domination. Its borders shifted west. Millions of people were displaced. The country’s wartime suffering did not end neatly with victory in 1945.
That is one reason the events of September 1939 remain so important. They reveal how war can begin through a chain of choices: aggressive ideology, diplomatic failure, secret agreements, false claims, and the belief that other countries will not act in time.
They also show that military defeat does not erase national resistance. Poland lost the 1939 campaign, but Polish people continued to fight in exile, in underground networks, and in Allied forces.
Key dates from the invasion of Poland
Date | Event |
23 August 1939 | Germany and the Soviet Union signed the Nazi-Soviet Pact. |
1 September 1939 | Germany invaded Poland. |
3 September 1939 | Britain and France declared war on Germany. |
17 September 1939 | The Soviet Union invaded eastern Poland. |
28 September 1939 | Warsaw surrendered after heavy bombardment. |
6 October 1939 | The final major fighting of the Polish campaign ended at Kock. |
Why 1939 still matters
History often gets reduced to dates, maps, and the movements of armies. The invasion of Poland deserves more than that. It was the moment when threats became open war, when promises were tested, and when civilians began paying the price for decisions made by dictators and governments.
The story also warns against accepting aggression as a local problem that can be contained by sacrificing another country’s freedom. Poland’s experience showed that unchecked expansion grows more dangerous, not less.
It is easy to look back and imagine the outcome was obvious. It was not. Leaders made choices under pressure. Some delayed. Some misread Hitler’s intentions. Some placed faith in agreements that aggressive powers had no intention of respecting. The result was a war that reshaped the twentieth century.
The invasion of Poland in 1939 began as a planned act of aggression by Nazi Germany. Within days, it had drawn Britain and France into war. Within weeks, Poland was divided between two dictatorships. Within years, the conflict had engulfed much of the world.
The central lesson is stark: the Second World War in Europe began not with a misunderstanding, but with an invasion. Poland was the first battlefield of a wider war, and its resistance became part of the Allied struggle from the very beginning.
Comments