The attack on Poland was an initial victory for Germany that surpassed the staff’s initial expectations, but it also galvanized Polish military resistance with the formation of a strong partisan underground that would never flag during the course of World War II and a Polish army in exile that would fight alongside the Allies at major engagements that included Operation Market Garden and the Battle of Monte Cassino.

Resistors and Jews were rounded up and sent to concentration camps. Tens of thousands of Poles died in the invasion, the first of some 50 million men, women and children who would lose their lives in World War II. It was just the beginning of the suffering for the Polish people, who were victims of some of the greatest horrors in a monstrous war.

The end result was often the same in both regimes: deportation, exploitation and, in many cases, death. Around one million Poles were deported from eastern Poland by the Soviets to the wilds of Siberia in that two-year period.

While the Nazis carried out their plan to strengthen the German “race”—purging the Reich of Jews, Sinti and Roma, the mentally and physically disabled, and others they considered defective or racially inferior—the invasion of Poland marked the start of the next phase of the Nazi racial program: the acquisition of Lebensraum, or “living space.”