June 21, 1941 – Germany launches the largest invasion in history as four million troops storm across the Russian border.
The Russians are initially caught off guard, enabling the Germans to capture a large swathe of Soviet territory, but they are eventually held up by determined Russian resistance outside the key cities of Moscow, Leningrad and Stalingrad.
The invasion of the Soviet Union marks a huge escalation in the European war.
The operation is driven by Adolf Hitler’s ideological desire to conquer Soviet territory as outlined in his 1925 manifesto Mein Kampf (“My Struggle”).
In the two years leading up to the invasion, the two countries sign political and economic pacts for strategic purposes. Nevertheless, Hitler authorizes an invasion of the Soviet Union. The Axis powers invade the Soviet Union along a 2,900-kilometer (1,800 mi) front, the largest invasion force in the history of warfare. In addition to troops, the Germans employ some 600,000 motor vehicles and between 600,000 and 700,000 horses. It marked the beginning of the rapid escalation of the war, both geographically and in the formation of the Allied coalition.
The failure of Operation Barbarossa was a turning point in the fortunes of the Third Reich. Most importantly, the operation opens up the Eastern Front, to which more forces are committed than in any other theater of war in world history. The Eastern Front becomes the site of some of the largest battles, most horrific atrocities, and highest casualties for Soviets and Germans alike, all of which influence the course of both World War II and the subsequent history of the 20th century. The German forces capture millions of Soviet prisoners who are not granted protections stipulated in the Geneva Conventions. Most of them never return alive; Germany deliberately starves the prisoners to death as part of a “Hunger Plan” that aims to reduce the population of Eastern Europe and then re-populate it with ethnic Germans. Over a million Soviet Jews are murdered by Einsatzgruppen death squads and gassing as part of the Holocaust.