WW2 · SEP 1939
Why did Nazi Germany and the USSR sign a pact in 1939?
The seminar question: “Why would two sworn ideological enemies — fascism and communism — sign a pact?”
On 23 August 1939 Nazi Germany and the Soviet Union signed a non-aggression pact whose secret protocol divided Eastern Europe into spheres of influence. Germany invaded Poland on 1 September, Britain and France declared war on 3 September, and the Red Army crossed Poland’s eastern border on 17 September.
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In August 1939 Hitler and Stalin made a bargain that gave each of them room to pursue an immediate goal. Their regimes remained ideological enemies, and both leaders expected a later struggle. For the moment, however, Hitler wanted to attack Poland without facing the Soviet Union at the same time. Soviet grain, oil, and metals would also help Germany withstand a British blockade.
The short answer
- Soviet distrust after Munich. Munich had excluded the Soviet Union. Stalin doubted that Britain and France would make an effective anti-German alliance, whereas a deal with Germany offered time, territory, and distance from a future front.
- Hitler avoids two fronts. A neutral Soviet Union left Hitler free to attack Poland without an immediate war on two fronts and opened the way to Soviet trade. He expected Britain and France either to yield again or to fight without decisive effect.
- Danzig as pretext. Demands over Danzig and the Polish Corridor provided Hitler with a public pretext. His larger purpose was Lebensraum, or living space, and the destruction of independent Poland.
THE TURNING POINT
First shots, 1 September, 04:47. The battleship Schleswig-Holstein opened fire on the Polish depot at Westerplatte at 04:47 on 1 September. The 182 defenders held out for seven days. Their stand could not turn back the invasion, but it makes clear that rapid defeat and determined resistance could occur together.
What it changed
The Phoney War begins. For eight months after Britain and France entered the war, the western land front was largely inactive. During this “Phoney War,” Germany had time to prepare its next campaign.
Two systems of occupation. Partition exposed Poles to two systems of occupation. Nazi authorities targeted Polish elites, clergy, and Jews from the beginning; Soviet authorities deported hundreds of thousands and murdered about 22,000 Polish officers and prisoners at Katyn and related sites. Poland suffered the war’s highest proportional national loss.
The USSR expands its buffer. The Soviet Union absorbed eastern Poland and then attacked Finland. Finnish resistance exposed weaknesses in Soviet forces, encouraging Hitler’s later, mistaken confidence that the USSR would collapse.
The full answer, argued
Each leader expected an immediate benefit from postponing their ideological conflict. Hitler could attack Poland without a Soviet war and obtain raw materials. Stalin gained time, territory, and a wider buffer while Germany fought the Western powers. Both expected a later confrontation, but for now each judged the bargain useful.
An interesting fact
Polish mathematicians had been quietly breaking the German Enigma cipher since 1932. Five weeks before the invasion, Polish military intelligence brought British and French officers to a bunker in the Kabaty woods south of Warsaw and gave each delegation a working replica of the machine. Bletchley Park’s wartime codebreaking built directly on that gift. Poland’s state disappeared from the map within weeks, yet the mathematics carried out that July helped destroy its occupier six years later.
This is the study layer of Invasion of Poland, chapter 2 of The War Room — WW2, 1936–1945; the full index of the atlas is here.
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