In August 1939, Germany and the Soviet Union signed a ten-year nonaggression pact, agreeing that neither would attach the other.  Hilter never intended to uphold his end of the deal, and on June 22, 1941, Germany invaded the Soviet Union.  Code-named Operation Barbarossa, the invasion was the largest German military operation of World War II.  With three million of its own troops and half a million of its allies’, Germany launched an attack across a broad front – from the Baltic Sea to the Black Sea – that caught the Soviet military off guard.  Hitler’s goal was to destroy the Soviet Union and to wipe out the racial and political enemies who lived there.  He pursed the latter by sending Einstazgruppen (mobile killing units) into Soviet territory behind his armies.

Composed of members of the Security Police (Sipo) and Security Service (SD) – and later, some Waffen-SS – the Einsatzgruppen were arranged into four groups (A, B, C, and D) that set out to track down Jews, Roma, Soviet and Communist officials, and the mentally disabled.  Initially, the killing squads executed only Communist officials and able-bodies Jewish men, but by August 1941, they were killing men, women, and children.

Standard procedure was for an Einsatzgruppe commander to coordinate a mass killing with the army unit in charge of a particular area.  Local collaborators often provided assistance as well.  Jews were marched or driven in trucks to an execution site and were forced to dig pits (i.e., mass graves), unless prisoners of war had already dug them.  The Jews were forced to undress and give up their valuables and were then shot.  It is estimated that by the spring of 1943, the Einsatzgruppen had murdered more than a million Jews.