A barrage of artillery fire extending over a front that was 1,200 miles long launched Germany’s invasion of the Soviet Union in the wee hours of June 22, 1941. Panzer and motorized divisions charged onto enemy soil, while bomber planes began to strike nearby Soviet airfields and distant naval bases. The Wehrmacht had amassed more than three million soldiers for this, the most powerful military assault in human history.

Operation Barbarossa — code-named after a medieval German emperor who, in addition to championing expansion into Eastern Europe, led a crusade to the Holy Land — was no ordinary war. Hitler saw it as a gigantic showdown between two rival ideologies that were contending for global supremacy: Nazism and Soviet communism (or “Judeo-Bolshevism” in his parlance).

In Nazi eyes, communism was a deadly weapon that Jewish intellectuals had forged to harm the world’s most developed races — the German people above all. For Germany to flourish, communism had to die. In the fight against Bolshevik “criminals,” Hitler explained to his generals ahead of the invasion, military conventions held no worth: “The communist is not a comrade beforehand and not a comrade afterwards. It is a war of extermination.”