Originally a place in which non-combatants were accommodated, as instituted by Lord Kitchener during the Second Boer War (1899–1902). The Boers, mainly women and children, were placed there officially for their own protection from Kitchener’s ‘scorched earth policy’ in the Transvaal and Cape Colony, but actually to prevent them from aiding the guerrillas. Some 20,000 detainees died, largely as a result of disease arising from unhygienic conditions.

During the Nazi regime in Germany (1933–45) concentration camps became places in which to intern unwanted persons, specifically Jewish people, but also Protestant and Catholic dissidents, communists, gypsies, trade unionists, homosexuals, and people with disabilities. Described by Goebbels in August 1934 as ‘camps to turn anti-social members of society into useful members by the most humane means possible’, they in fact came to witness depraved acts of torture, slave labour, horror, and mass murder on a scale unprecedented in any country in any century. Some 200,000 had been through the camps before World War II began, when they were increased in size and number. The camps (Konzetrazionslager, or KZ), administered by the SS, were categorized into Arbeitslager, where prisoners were organized into labour battalions, and Vernichtungslager, set up for the extermination and incineration of men, women, and children. In eastern Europe prisoners were used initially in labour battalions or in the tasks of genocide, until they too were exterminated. In such camps as Auschwitz, gas chambers could kill and incinerate 12,000 people daily. In the west, Belsen, Dachau, and Buchenwald (a forced labour camp where doctors conducted medical research on prisoners) were notorious. An estimated six million Jews died in the camps (the Holocaust), as well as some half million gypsies; in addition, millions of Poles, Soviet prisoners-of-war, and other civilians perished. After the war many camp officials were tried and punished, but others escaped. Maidanek was the first camp to be liberated (by the Red Army, in July 1944). After 1953 West Germany paid $37 billion in reparations to the surviving Jewish victims of Nazism.

In the Soviet Union, Lenin greatly enlarged (1919) the Tsarist forced labour camps, which were renamed Gulags (Russian acronym for the Main Administration of Corrective Labour Camps) in 1930. An estimated 15 million prisoners were confined to the Gulags during Stalin’s purges, of whom many succumbed to disease, famine, or the firing squad.