The Holocaust was the systematic, bureaucratic, state-sponsored persecution and murder of six million Jews by the Nazi regime and its collaborators. "Holocaust" is a word of Greek origin meaning "sacrifice by fire." The Nazis, who came to power in Germany in January 1933, believed that Germans were "racially superior" and that the Jews, deemed "inferior," were an alien threat to the so-called German racial community. German authorities also targeted other groups because of their perceived "racial inferiority": Roma (Gypsies), the disabled, and some of the Slavic peoples (Poles, Russians, and others). Other groups were persecuted on political, ideological, and behavioral grounds, among them Communists, Socialists, Jehovah's Witnesses, and homosexuals.
In the early years of the Nazi regime, the National Socialist government established concentration camps to detain real and imagined political and ideological opponents. Following the invasion of the Soviet Union in June 1941, Einsatzgruppen (mobile killing units) moved behind German lines to carry out mass-murder operations against Jews, Roma, and Soviet state and Communist Party officials. German SS, police, and military units murdered more than a million Jewish men, women, and children, and hundreds of thousands of others. Between 1941 and 1944, Nazi German authorities deported millions of Jews from Germany, from occupied territories, and from the countries of many of its Axis allies to ghettos and to killing centers, often called extermination camps, where they were murdered in specially developed gassing facilities. In 1933, the Jewish population of Europe stood at over nine million. By 1945, the Germans and their collaborators had killed nearly two out of every three European Jews as part of the "Final Solution," the Nazi policy to murder the Jews of Europe.