According to the United States Holocaust Memorial Museum, the first camps were called concentration camps because they physically concentrated “German Communists, Socialists, Social Democrats, Roma (Gypsies), Jehovah's Witnesses, homosexuals, and those accused of ‘asocial’ or socially deviant behavior.” The first mass deportation of Jews to concentration camps did not occur until after Kristallnacht in November 1938.
In 1939, after the German invasion of Poland, Nazis opened forced-labor camps. In these camps, prisoners died from exhaustion, starvation and exposure to the elements. In 1941, after the German invasion of the Soviet Union, some concentration camps were turned into death camps and killing centers, as it was considered the most “efficient” way to achieve the “Final Solution to the Jewish Question.”
Treblinka was one of five killing centers. Auschwitz, also located in Nazi-occupied Poland, was the largest mass murder site in history. Gas chambers were built in a section of the camp called Birkenau. At Auschwitz-Birkenau, at least 960,000 Jews, 74,000 Poles, 21,000 Roma, 15,000 Soviet prisoners of war, and 15,000 people of other nationalities were killed, many in the gas chambers.