Extermination camps (or death camps) were camps during World War II (1939–45) built primarily but not exclusively by Nazi Germany to systematically kill millions of people by execution (primarily by gassing) and extreme work under starvation conditions. While there were victims from many groups, Jews were the main Nazi targets. This genocide of the Jewish people was the Third Reich's "Final Solution to the Jewish question". The Nazi attempts at Jewish genocide are collectively known as the Holocaust.