Under the codename Operation "Barbarossa," Nazi Germany invaded the Soviet Union on June 22, 1941, in the largest German military operation of World War II.
The destruction of the Soviet Union by military force, the permanent elimination of the perceived Communist threat to Germany, and the seizure of prime land within Soviet borders for long-term German settlement had been a core policy of the Nazi movement since the 1920s. Adolf Hitler had always regarded the German-Soviet nonaggression pact, signed on August 23, 1939, as a temporary tactical maneuver. In July 1940, just weeks after the German conquest of France and the Low Countries, Hitler decided to attack the Soviet Union within the following year. On December 18, 1940, he signed Directive 21 (code-named Operation "Barbarossa"), the first operational order for the invasion of the Soviet Union.
From the beginning of operational planning, German military and police authorities intended to wage a war of annihilation against the Communist state as well as the Jews of the Soviet Union, whom they characterized as forming the "racial basis" for the Soviet state. During the winter and spring months of 1941, officials of the Army High Command (Oberkommando des Heeres-OKH) and the Reich Security Main Office (Reichssicherheitshauptamt-RSHA) negotiated arrangements for the deployment of special units (Einsatzgruppen) of the Security Police and the Security Service (Sicherheitsdienst-SD) behind the front lines to physically annihilate Jews, Communists and other persons deemed to be dangerous to establishment of long-term German rule on Soviet territory.
With 134 Divisions at full fighting strength and 73 more divisions for deployment behind the front, German forces invaded the Soviet Union on June 22, 1941, less than two years after the German-Soviet Pact was signed. Three army groups, including more than three million German soldiers, supported by 650,000 troops from Germany's allies (Finland and Romania), and later augmented by units from Italy, Croatia, Slovakia and Hungary, attacked the Soviet Union across a broad front, from the Baltic Sea in the north to the Black Sea in the south. For months, the Soviet leadership had refused to heed warnings from the Western Powers of the German troop buildup along its western border. Germany and its Axis partners thus achieved almost complete tactical surprise. Much of the existing Soviet air force was destroyed on the ground; the Soviet armies were initially overwhelmed. German units encircled millions of Soviet soldiers, who, cut off from supplies and reinforcements, had few options other than to surrender.
As the German army advanced deep into Soviet territory, SS and police units followed the troops. The first to arrive were the Einsatzgruppen of the Security Police and the SD, which the RSHA tasked with identifying and eliminating persons who might organize and implement resistance to the German occupation forces, identifying and concentrating groups of people who were "hostile" to German rule in the East, establishing intelligence networks, and securing key documentation and facilities.
Often known as mobile killing units, the Einsatzgruppen initiated mass-murder operations, primarily against Jewish males, officials of the Communist Party and State and Soviet Roma, and, often with assistance from German Army personnel, established ghettos and other holding facilities to concentrate large numbers of Soviet Jews.
Beginning in late July, with the arrival of Himmler's representatives, the Higher SS and Police Leaders and significant reinforcement, the SS and police, supported by locally recruited auxiliaries, began to physically annihilate entire Jewish communities in the Soviet Union. Success both on the military front and in the murder of the Soviet Jews contributed to Hitler's decision to deport German Jews to the occupied Soviet Union beginning on October 15, 1941, initiating what would become "Final Solution" policy: the physical annihilation of the European Jews.
Despite catastrophic losses in the first six weeks of the war, the Soviet Union failed to collapse as anticipated by the Nazi leadership and the German military commanders. In mid-August 1941, Soviet resistance stiffened, knocking the Germans off of their unrealistic timetable. Nevertheless, by late September 1941, German forces reached the gates of Leningrad in the north. They took Smolensk in the center and Dnepropetrovsk (Dnipropetrovs'k) in Ukraine. They spilled into the Crimean Peninsula in the south. German units reached the outskirts of Moscow in early December.
Yet after months of campaigning, the German army was exhausted. Having expected a rapid Soviet collapse, German planners had failed to equip their troops for winter warfare. Expecting their military personnel to live off the land of a conquered Soviet Union at the expense of the indigenous population, which in German calculations, would starve to death in the millions, German planners had failed to provide sufficient food and medicines. Worse still, German troops, advancing rapidly, outran their supply lines, rendering thinly defended flanks vulnerable to Soviet counterattack along the 1,000 mile stretch from Berlin to Moscow.
On December 6, 1941, the Soviet Union launched a major counterattack against the center of the front, driving the Germans back from Moscow in chaos. Only weeks later were the Germans able to stabilize the front east of Smolensk. In the summer of 1942, Germany resumed the offensive with a massive attack to the south and southeast toward the city of Stalingrad (Volgograd) on the Volga River and toward the oil fields of the Caucasus. As the Germans reached the outskirts of Stalingrad and approached Groznyj (Groznyy) in the Caucasus, approximately 120 miles from the shores of the Caspian Sea in September 1942, the German domination of Europe reached its furthest geographical extension.