In August 1939, Germany signed a mutual non-aggression pact with the Soviet Union, then led by Joseph Stalin, in which the two nations agreed not to take military action against each other for a period of 10 years.

Given the long history of bitter conflict between the two nations, the Molotov-Ribbentrop Pact surprised the world and dismayed France and Britain, who had signed their own agreement with Hitler’s regime only to see it violated when Germany invaded Czechoslovakia earlier that year.

Hitler wanted to neutralize an existing mutual defense treaty between France and the Soviet Union and ensure the Soviets would stand by when Germany invaded its next target: Poland. The pact included secret plans to divide Poland into spheres of influence, with Germany annexing the western half of the country and the Soviet Union the east.

On September 3, 1939, two days after Nazi Germany invaded Poland, France and Britain declared war on Germany. After eight months of so-called phony war, Germany launched its blitzkrieg (“lightning war”) through Western Europe, conquering Belgium, the Netherlands, Luxembourg and France in just six weeks beginning in May 1940.

With France defeated and only Britain left standing against Germany in Western Europe, Hitler turned toward his next goal—Germany’s expansion into the Eastern Front, and the lebensraum (“living space”) that would ensure the dominance of the German people.

By definition, this required the defeat of the Soviet Union and the colonization of its territories, especially the resource-rich Ukraine, by “Aryan” Germans rather than its native Slavic population, which Hitler viewed as racially inferior.

By the end of 1940, Hitler had issued Führer Directive 21, an order for Germany’s planned invasion of the Soviet Union. Codenamed Operation Barbarossa—after the nickname of the powerful Medieval Holy Roman Emperor Frederick I—the invasion called for German troops to advance along a line running north-south from the port of Archangel to the port of Astrakhan on the Volga River, near the Caspian Sea.

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Hitler hoped to repeat the success of the blitzkrieg in Western Europe and win a quick victory over the massive nation he viewed as Germany’s sworn enemy.

On June 22, 1941, more than 3 million German and Axis troops invaded the Soviet Union along an 1,800-mile-long front, launching Operation Barbarossa. It was Germany’s largest invasion force of the war, representing some 80 percent of the Wehrmacht, the German armed forces, and one of the most powerful invasion forces in history.

Despite repeated warnings, Stalin refused to believe that Hitler was planning an attack, and the German invasion caught the Red Army unprepared. With a three-pronged attack toward Leningrad in the north, Moscow in the center and Ukraine in the south, German Panzer tank divisions and Luftwaffe air bombardments helped Germany gain an early advantage against the numerous but poorly trained Soviet troops.

On the first day of the attack alone, the Luftwaffe managed to shoot down more than 1,000 Soviet aircraft.

German forces initially moved quickly along the vast front, taking millions of Soviet soldiers as prisoners. The Einsatzgruppen, or armed SS death squads, followed in the army’s wake, seeking out and killing many civilians, especially Soviet Jews.

Hitler’s directives for the invasion included the Commissar Order, which authorized the immediate execution of all captured enemy officers. Many Soviet prisoners of war were also killed immediately upon capture, another practice that violated international war protocols.

While they made territorial gains, German forces also sustained heavy casualties, as the Soviets’ numerical advantage and the strength of their resistance proved greater than expected. By the end of August, with German Panzer divisions just 220 miles from the Soviet capital, Hitler ordered—over the protests of his generals—that the drive against Moscow be delayed in favor of focusing on Ukraine to the south.

Kiev, Ukraine, fell to the Wehrmacht by the end of September 1941. In the north, Germans managed (with aid of Finnish allies) to cut Leningrad off from the rest of Russia, but they weren’t strong enough to take the city itself. Instead, Hitler ordered his forces to starve Leningrad into submission, beginning a siege that would end up lasting some 872 days.

In early October 1941, Hitler ordered the launch of Operation Typhoon, the German offensive against Moscow. The delay had given the Soviets time to strengthen the defense of their capital with some 1 million troops and 1,000 new T-34 tanks. After a successful initial assault, the muddy roads of autumn—known as Rasputitsa, or quagmire season—literally stalled the German offensive outside Moscow, where they ran into the improved Russian defenses.

In mid-November, Panzer divisions attempted a final attempt to encircle Moscow, getting within 12 miles of the city. But reinforcements from Siberia helped the Red Army beat back the attack, halting the German offensive for good as the brutal winter weather arrived. Soviet forces mounted a surprise counterattack in early December, putting the Germans on the defensive and forcing them into retreat.

Despite its territorial gains and the damage inflicted on the Red Army, Operation Barbarossa failed in its primary objective: to force the Soviet Union to capitulate.

Though Hitler blamed the winter weather for the failure of the Moscow offensive, the entire operation had suffered from a lack of long-term strategic planning. Counting on a quick victory, the Germans had failed to set up adequate supply lines to deal with the vast distances, icy weather and harsh terrain.

They had also underestimated the strength of the Soviet resistance, which Stalin skillfully encouraged with his calls to defend “Mother Russia.” Hitler’s Commissar Order and other ruthless behavior on the part of the Germans also served to solidify the Red Army’s determination to fight until the end.

Fighting was far from over on the Eastern Front, and Hitler ordered another major strategic offensive against the Soviet Union in June 1942. Thanks to similar obstacles, it eventually met with failure as well, with the Battle of Stalingrad in 1943 helping turn the tide decisively toward the Allied Powers in World War II.

READ MORE: How Did World War II End?

Operation Barbarossa and Germany’s Failure in the Soviet Union. Imperial War Museums.
Anthony Beevor, “Operation Barbarossa: why Hitler’s invasion of the Soviet Union was his greatest mistake.” BBC: History Extra, March 3, 2021.
Norman Stone, World War II: A Short History. (Basic Books, 2013).