Nazi Germany maintained concentration camps (in German Konzentrationslager, or KZ) throughout the territories it controlled. The first Nazi concentration camps set up in Germany were greatly expanded after the Reichstag fire of 1933, and were intended to hold political prisoners and opponents of the regime. The term was borrowed from the British concentration camps of the Second Anglo-Boer War.
The number of camps quadrupled between 1939 and 1942, as slave-laborers from across Europe, Jews, political prisoners, criminals, homosexuals, gypsies, the mentally ill and others were incarcerated, generally without judicial process. Holocaust scholars draw a distinction between concentration camps and extermination camps, which were established by the Nazis for the industrial-scale mass murder of the predominantly Jewish ghetto and concentration camp populations.
After September 1939, with the beginning of the Second World War, concentration camps became places where millions of ordinary people were enslaved as part of the war effort, often starved, tortured and killed. During the War, new Nazi concentration camps for "undesirables" spread throughout the continent. According to statistics by the German Ministry of Justice, about 1,200 camps and subcamps were run in countries occupied by Nazi Germany, while the Jewish Virtual Library estimates that the number of Nazis camps was closer to 15,000 in all of occupied Europe and that many of these camps were created for a limited time before being demolished. Camps were being created near the centers of dense populations, often focusing on areas with large communities of Jews, Polish intelligentsia, Communists or Roma. Since millions of Jews lived in pre-war Poland, most camps were located in the area of General Government in occupied Poland, for logistical reasons. The location also allowed the Nazis to quickly remove the German Jews from within the German proper. In 1942, the SS built a network of Extermination camps to systematically kill millions of prisoners by gassing. The extermination camps (Vernichtungslager) and death camps (Todeslager) were camps whose primary function was genocide. The Nazis themselves distinguished between concentration camps and the extermination camps.
According to Moshe Lifshitz, the Nazi camps divided as follows: Hostage camps (or death camps): camps where hostages were held and killed as reprisals. Labor camps: concentration camps where interned inmates had to do hard physical labor under inhumane conditions and cruel treatment. Some of these camps were sub-camps of bigger camps, or "operational camps", established for a temporary need. POW camps: concentration camps where prisoners of war were held after capture. These POW's endured torture and liquidation on a large scale. Camps for rehabilitation and re-education of Poles: camps where the intelligentsia of the ethnic Poles were held, and "re-educated" according to Nazi values as slaves. Transit and collection camps: camps where inmates were collected and routed to main camps, or temporarily held (Durchgangslager or Dulag). Extermination camps: These camps differed from the rest, since not all of them were also concentration camps. Although none of the categories is independent, and each camp could be classified as a mixture of several of the above, and all camps had some of the elements of an extermination camp, systematic extermination of new-arrivals occurred in very specific camps. Of these, four were extermination camps, where all new-arrivals were simply killed -- the "Aktion Reinhard" camps (Treblinka, Sobibor and Belzec), together with Chelmno. Two others (Auschwitz and Majdanek) were combined concentration and extermination camps. Others were at times classified as "minor extermination camps".
