 The Nazi "Endlösung der Judenfrage" (The Final Solution of the Jewish Question), based on the systematic killing of Europe's Jews by gassing, began during Operation Reinhard, after the onset of the Nazi-Soviet war of June 1941.The adoption of the gassing technology by Nazi Germany was preceded by a wave of hands-on killings carried out by the SS "Einsatzgruppen", who followed the Wehrmacht army during Operation Barbarossa on the Eastern Front.The camps designed specifically for the mass gassings of Jews were established in the months following the Wannsee Conference chaired by Reinhard Heydrich in January 1942 in which the principle was made clear that the Jews of Europe were to be exterminated.