Invasion of Poland (1939): How World War II Began in Europe

The invasion of Poland was the attack on Poland by Nazi Germany beginning on 1 September 1939, joined by the Soviet Union from 17 September. It led Britain and France to declare war on Germany on 3 September and is generally taken as the start of the Second World War in Europe. Within about five weeks the Polish army had been defeated and the country was divided between its two neighbours, opening a long and brutal occupation.

Background: Danzig, the Corridor and the pact

The peace settlement after the First World War recreated an independent Poland and gave it access to the Baltic Sea through a strip of land known as the Polish Corridor. The mainly German port city of Danzig (Gdańsk) became a Free City under League of Nations protection, a compromise laid down in the Treaty of Versailles. Many Germans resented these arrangements, and Nazi propaganda exploited them throughout the 1930s.

After annexing Austria and, following the Munich Agreement, the Sudetenland, Hitler occupied the rest of Bohemia and Moravia in March 1939. He then pressed Poland to hand over Danzig and allow an extraterritorial road and railway across the Corridor. The Polish government under Foreign Minister Józef Beck refused. On 31 March 1939 Britain, soon joined by France, publicly guaranteed Polish independence.

The decisive step came on 23 August 1939, when Germany and the Soviet Union signed a non-aggression treaty in Moscow, known as the Molotov-Ribbentrop Pact. A secret protocol divided Eastern Europe into spheres of influence and drew a line through Poland along the Narew, Vistula and San rivers. Hitler now expected to avoid a two-front war. Britain answered by signing a formal mutual assistance agreement with Poland on 25 August.

The plan and the forces

Germany’s plan, codenamed Fall Weiss (Case White), was to encircle and destroy the Polish army west of the Vistula. Army Group North under Fedor von Bock attacked from Pomerania and East Prussia, while Army Group South under Gerd von Rundstedt advanced from Silesia and from Slovakia, which also sent its own troops. In total Germany committed roughly 1.5 million men, around 2,500 to 2,800 tanks and nearly 2,000 combat aircraft.

Poland, commanded by Marshal Edward Rydz-Śmigły, had a long and exposed frontier to defend. Its general mobilisation had been delayed under Allied pressure and was incomplete when the attack began, so only part of its strength of around one million men was in place. The Polish army had about 800 to 900 tanks and tankettes, mostly light, and some 400 front-line aircraft. It chose to defend close to the border to protect its industrial regions, which left its armies vulnerable to being outflanked.

What happened

On the evening of 31 August SS men staged a fake Polish attack on the German radio station at Gleiwitz (Gliwice), one of several incidents meant to give Germany a pretext. In the early hours of 1 September German bombers struck the small town of Wieluń, and the old battleship Schleswig-Holstein opened fire on the Polish depot at Westerplatte in Danzig. German troops crossed the frontier along its whole length that morning.

Germany combined fast armoured and motorised columns with heavy air attacks on roads, railways, airfields and towns. Polish units fought hard in many places, for example at Mława in the north and at Mokra in the south-west, but German forces broke through the frontier defences within days. Columns of refugees crowded the roads eastwards, where they were often strafed from the air, and communications between the Polish high command and its armies repeatedly broke down. Kraków fell on 6 September and German tanks reached the outskirts of Warsaw on 8 September, where they were beaten back.

On 3 September Britain and France declared war on Germany, followed by Australia and New Zealand the same day, and later by South Africa and Canada. Yet no relief reached Poland. A cautious French advance into the Saarland from 7 September was halted after a few kilometres and later withdrawn, and the Royal Air Force dropped mainly leaflets over Germany.

The largest battle of the campaign began on 9 September along the Bzura river west of Warsaw. General Tadeusz Kutrzeba’s Poznań Army, together with the Pomorze Army, struck the flank of the German forces advancing on the capital. The counter-attack achieved early success but was crushed by German reinforcements and air power, and the battle ended around 22 September with the loss of most of the Polish forces involved.

On 17 September the Red Army invaded eastern Poland under the terms of the secret protocol, in what became the Soviet invasion of Poland. With almost no reserves left to defend the east, the Polish government and high command crossed into Romania, where they were interned. Warsaw, heavily bombed and shelled and short of water and food, surrendered on 28 September. The fortress of Modlin fell the next day, the Hel peninsula on 2 October, and the last major Polish formation under General Franciszek Kleeberg laid down its arms after the Battle of Kock on 6 October.

Key people

• Adolf Hitler, German dictator, who ordered the attack and intended from the outset to destroy the Polish state.
• Marshal Edward Rydz-Śmigły, Polish commander-in-chief, criticised afterwards for the forward deployment and for leaving the country.
• Gerd von Rundstedt and Fedor von Bock, commanders of the German army groups.
• General Tadeusz Kutrzeba, architect of the Bzura counter-offensive and later a defender of Warsaw.
• Władysław Sikorski, who became prime minister of the Polish government-in-exile formed in France at the end of September.

Occupation and consequences

On 28 September Germany and the Soviet Union signed a Boundary and Friendship Treaty that adjusted their dividing line, moving it east to the Bug river in exchange for placing Lithuania in the Soviet sphere. Germany annexed western Poland directly and turned the central region into the General Government, ruled from Kraków by Hans Frank. The Soviet Union incorporated the eastern half into the Ukrainian and Belorussian Soviet republics.

German rule was marked from the first weeks by mass violence. Einsatzgruppen (SS and police task forces) and other units killed tens of thousands of Polish civilians, including teachers, priests, landowners and political leaders, in operations intended to eliminate Poland’s educated class. Jews were subjected to violence, forced labour and ghettoisation, the first stage of what became the Holocaust. In the Soviet zone, arrests and mass deportations followed, and in 1940 the NKVD murdered some 22,000 Polish officers and other prisoners in the Katyn massacre.

Poland never surrendered as a state. A government-in-exile continued the war from France and then Britain, and tens of thousands of Polish soldiers and airmen escaped through Romania and Hungary to fight on in the west. An underground state and resistance movement grew inside the country. In western Europe, the months after the campaign became known as the Phoney War, a period of little fighting that ended with Germany’s attacks on Scandinavia and France in 1940.

Myths and facts

Myth: Polish cavalry charged German tanks with lances. At Krojanty on 1 September 1939 Polish lancers charged a German infantry unit and were then fired on by armoured cars. Journalists and propagandists later turned this into a legend of horsemen attacking tanks. Polish cavalry normally fought dismounted, as mobile infantry with anti-tank guns.

Myth: the Polish air force was destroyed on the ground on the first day. Most Polish combat aircraft had already been dispersed to secret airfields before the attack. They fought for about two weeks against a much larger and more modern Luftwaffe, and many surviving aircraft were flown to Romania.

Myth: the campaign proved a new “Blitzkrieg” doctrine. Germany did use tanks, motorised infantry and aircraft very effectively, but “Blitzkrieg” was a journalistic label rather than an official doctrine. Much of the German army still marched on foot and relied on horse-drawn transport.

By the numbers

Estimates vary between sources, especially for civilian deaths, which most historians put well above 100,000 for the campaign itself.

Timeline

• 1939, 23 August: Germany and the Soviet Union sign the Molotov-Ribbentrop Pact with its secret protocol.
• 1939, 25 August: Britain and Poland sign an agreement of mutual assistance.
• 1939, 1 September: Germany attacks Poland; Wieluń is bombed and Westerplatte is shelled.
• 1939, 3 September: Britain and France declare war on Germany.
• 1939, 9 September: The Battle of the Bzura begins.
• 1939, 17 September: The Soviet Union invades eastern Poland.
• 1939, 28 September: Warsaw surrenders; Germany and the Soviet Union sign the Boundary and Friendship Treaty.
• 1939, 6 October: The last Polish field force capitulates after the Battle of Kock.

Why it matters

The invasion of Poland turned a series of European crises into a general war that eventually spread across the world. It showed the destructive power of modern combined-arms warfare and the emptiness of guarantees that could not be enforced. Above all, it began an occupation in which Poland lost an estimated 5 to 6 million citizens, roughly one in six of its pre-war population, including the great majority of its Jewish citizens, by 1945.