The idea of mass extermination with the use of stationary facilities to which the victims were taken by train , was the result of earlier Nazi experimentation with chemically manufactured poison gas during the secretive Aktion T4 euthanasia programme against hospital patients with mental and physical disabilities . The technology was adapted , expanded , and applied in wartime to unsuspecting victims of many ethnic and national groups ; the Jews were the primary target , accounting for over 90 percent of the extermination camp death toll . The genocide of the Jews of Europe was the Third Reich 's " Final Solution to the Jewish question " . It is now collectively known as the Holocaust , during which 11 million others were also murdered . Extermination camps were also set up by the fascist Ustaše regime of the Independent State of Croatia , a puppet state of Germany , which carried out genocide between 1941 and 1945 against Serbs , Jews , Roma and its Croat and Bosniak Muslim political opponents
the Holocaust
The Holocaust
Extermination camp