During the Holocaust
, the Nazis established concentration camps across Europe. At first, these concentrations camps were meant to hold political prisoners; however, by the beginning of World War II, these concentration camps had transformed and expanded in order to house vast numbers of non-political prisoners whom the Nazis exploited through forced labor. Many concentration camp prisoners died from the horrible living conditions or from being literally worked to death.
By 1941, the Nazis began building Chelmno, the first extermination camp (also called death camp), in order to "exterminate" both Jews and Gypsies. In 1942, three more death camps were built (Treblinka, Sobibor, and Belzec) and used solely for mass murder. Around this time, killing centers were also added at the concentration camps of Auschwitz and Majdanek.
It is estimated that the Nazis used these camps to kill an estimated 11 million people.