On September 1, 1939, the German army under Adolf Hitler launched an invasion of Poland that triggered the start of World War II (though by 1939 Japan and China were already at war). The battle for Poland only lasted about a month before a Nazi victory. But the invasion plunged the world into a war that would continue for almost six years and claim the lives of tens of millions of people.
Hitler salutes as he oversees troops during the Nazi occupation of Poland. The troops march in formation toward a wooden bridge, constructed by the Nazis across the San River, near Jarolaw, Poland
Today, 75 years later, Hitler is regarded as one of history’s great villains. So it’s easy to forget how slowly and reluctantly the worlds most powerful democracies mobilized to stop him. France and Britain did declare war on Germany two days after the invasion of Poland, but it would take them another eight months before they engaged in full-scale war with the Nazis. The United States wouldn’t join the war against Hitler until December 1941, a full two years after the war began.
Why did Adolf Hitler invade Poland?
The short answer is that Adolf Hitler was a ruthless dictator with dreams of conquering all of Europe. Annexing Poland was a step in that larger plan. The Polish military wasn’t powerful enough to resist him, and Hitler calculated — correctly, as it turns out — that Europe’s other powers wouldn’t intervene in time.
This map shows how World War I reshaped Europe. The red lines show the new borders drawn by the victorious Allies at the Paris Peace Conference of 1919
The invasion of Poland occurred almost exactly 25 years after the start of World War I in August 1914. That war ended in Germany’s defeat, and in 1919 the victorious allies carved up territory that had been part of Germany, Austria-Hungary (Germany’s defeated ally), and Russia (which had fallen to the Bolsheviks) into an array of new countries.
One of these new countries was Poland, which before 1919 had last existed as an independent nation in 1795. Another was Czechoslovakia — its awkward name reflects the Allies’ decision to combine areas dominated by two different ethnic groups, Czechs and Slovaks, into a single nation.
Hitler was contemptuous of these new nations, which he regarded as artificial creations of the Allies. There were significant German populations in both countries, and Hitler used trumped-up concern for their welfare as a pretext to demand territorial concessions.
In the infamous 1938 Munich Agreement, British Prime Minister Neville Chamberlain agreed to Hitler’s annexation of the Sudetenland, portions of of Czechoslovakia with ethnic-German majorities (Czechoslovakia itself was excluded from the negotiations). Chamberlain claimed that the deal had averted another massive European war, but it only delayed the conflict while making Hitler more powerful when the war finally came.