The Holocaust was the systematic annihilation of six million Jews by Adolf Hitler and the Nazis during World War 2. In 1933 approximately nine million Jews lived in the 21 countries of Europe that would be military occupied by Germany during the war. By 1945 two out of every three European Jews had been killed by the Nazis. 1.5 million children were murdered. This figure includes more than 1.2 million Jewish children, tens of thousands of Gypsy children and thousands of handicapped children.

Dachau was the first concentration camp established in Nazi Germany - the camp was opened on March 22, 1933. The first inmates were primarily political prisoners, Social Democrats, Communists, trade unionists, habitual criminals, homosexuals, Jehovah's Witnesses, beggars, vagrants, hawkers.

In the late 1930's the Nazis killed thousands of handicapped Germans by lethal injection and poisonous gas. After the German invasion of the Soviet Union in June 1941, mobile killing units following in the wake of the German Army began shooting massive numbers of Jews and Gypsies in open fields and ravines on the outskirts of conquered cities and towns. 

Eventually the Nazis created a more secluded and organized method of killing. Six extermination centers were established in occupied Poland - Auschwitz-Birkenau, Belzec, Chelmno, Majdanek, Sobibor, and Treblinka - where large-scale murder by gas and body disposal through cremation were conducted systematically. Victims were deported to these centers from Western Europe and from the ghettos in Eastern Europe which the Nazis had established. In addition, millions died in the ghettos and concentration camps as a result of forced labor, starvation, exposure, brutality, disease, and execution.