The Nazi camp system began as a system of repression directed against political opponents of the Nazi state. In the early years of the Third Reich, the Nazis imprisoned primarily Communists and Socialists. In about 1935, the regime also began to imprison those whom it designated as racially or biologically inferior, especially Jews. During World War II, the organization and scale of the Nazi camp system expanded rapidly and the purpose of the camps evolved beyond imprisonment toward forced labor and outright murder.
Throughout German-occupied Europe, the Germans arrested those who resisted their domination and those they judged to be racially inferior or politically unacceptable. People arrested for resisting German rule were mostly sent to forced-labor or concentration camps. The war brought unprecedented growth in both the number of camps and the number of prisoners. Within three years the number of prisoners quadrupled, from about 25,000 before the war to about 100,000 in March 1942. The camp population came to include prisoners from almost every European nation. Prisoners in all the concentration camps were literally worked to death. According to SS reports, there were more than 700,000 prisoners registered in the concentration camps in January 1945.
The Germans deported Jews from all over occupied Europe to extermination camps in Poland, where they were systematically killed, and also to concentration camps, where they were drafted for forced labor -- "extermination through work." Several hundred thousand Roma (Gypsies) and Soviet prisoners of war were also systematically murdered.U.S. Holocaust Memorial Museum