Concentration camp
More than half of the Jewish people who died in the Holocaust died at Nazi concentration camps.  Just in the Auschwitz camps, at least 1.1 million people died (about 1,000,000 Jews and about 75,000 non-Jewish people, like Poles).  Towards the end of World War II, the Nazis killed up to 20,000 people a day in the camps' gas chambers.