The Holocaust

An American soldier stands in front of a wagon piled high with corpses outside the crematorium in the newly liberated Buchenwald concentration camp

One of the foundations of Hitler's social policies was the concept of racial hygiene. It was based on the ideas of Arthur de Gobineau, a French count; eugenics, a pseudo-science that advocated racial purity; and social Darwinism. Applied to human beings, "survival of the fittest" was interpreted as requiring racial purity and killing off "life unworthy of life." The first victims were children with physical and developmental disabilities; those killings occurred in a programme dubbed Action T4.^[152] After a public outcry, Hitler made a show of ending this program, but the killings continued (see Nazi eugenics).
Between 1939 and 1945, the SS, assisted by collaborationist governments and recruits from occupied countries, systematically killed somewhere between 11 and 14 million people, including about six million Jews,^[153][154] in concentration camps, ghettos and mass executions, or through less systematic methods elsewhere. In addition to those gassed to death, many died as a result of starvation and disease while working as slave labourers (sometimes benefiting private German companies). Along with Jews, non-Jewish Poles, Communists and political opponents, members of resistance groups, homosexuals, Roma, the physically handicapped and mentally retarded, Soviet prisoners of war (possibly as many as three million), Jehovah's Witnesses, Adventists, trade unionists, and psychiatric patients were killed. One of the biggest centres of mass-killing was the industrial extermination camp complex of Auschwitz-Birkenau. As far as is known, Hitler never visited the concentration camps and did not speak publicly about the killing in precise terms.^[155]
The Holocaust (the "Endlösung der jüdischen Frage" or "Final Solution of the Jewish Question") was planned and ordered by leading Nazis, with Heinrich Himmler and Reinhard Heydrich playing key roles. While no specific order from Hitler authorizing the mass killing has surfaced, there is documentation showing that he approved the Einsatzgruppen killing squads that followed the German army through Poland and Russia, and that he was kept well informed about their activities. The evidence also suggests that in the fall of 1941 Himmler and Hitler decided upon mass extermination by gassing. During interrogations by Soviet intelligence officers declassified over fifty years later, Hitler's valet Heinz Linge and his military aide Otto Gunsche said Hitler had "pored over the first blueprints of gas chambers." His private secretary, Traudl Junge, testified that Hitler knew all about the death camps.^{[citation needed]}
Göring gave a written authorisation to Heydrich to "make all necessary preparations" for a "total solution of the Jewish question". To make for smoother cooperation in the implementation of this "Final Solution", the Wannsee conference was held on 20 January 1942, with fifteen senior officials participating (including Adolf Eichmann) and led by Reinhard Heydrich. The records of this meeting provide the clearest evidence of planning for the Holocaust. On 22 February, Hitler was recorded saying to his associates, "we shall regain our health only by eliminating the Jews".