The Nazis used the term "Final Solution" to refer to their plan to annihilate the Jewish people. In its entirety, the "Final Solution" called for the murder of all European Jews by gassing, shooting, and other means. Six million Jewish men, women, and children were killed during the Holocaust—two-thirds of the Jews living in Europe before World War II. The genocide or mass destruction of the Jews was the culmination of a decade of increasingly severe discriminatory measures. After the September 1939 German invasion of Poland (the beginning of World War II), anti-Jewish policy escalated to the imprisonment and eventual murder of European Jewry. After the June 1941 German invasion of the Soviet Union, SS and police units (acting as mobile killing units) began massive shooting operations aimed at entire Jewish communities. By autumn 1941, the SS and police introduced mobile gas vans with the exhaust pipe reconfigured to pump poisonous carbon monoxide gas into sealed spaces, killing those locked within.
German SS and police murdered nearly 2,700,000 Jews in killing centers either by asphyxiation with poison gas or by shooting. Three killing centers, with no purpose other than mass murder, were established in German occupied Poland—Belzec, Sobibor, and Treblinka. Other Nazi camps were also the site of mass murder as part of the "Final Solution." The Majdanek camp had gas chambers, in which the SS killed tens of thousands of Jews, primarily forced laborers too weak to work. SS and police killed at least 152,000 people, mostly Jews, but including a few thousand Roma (Gypsies) in gas vans at the Chelmno killing center. SS authorities murdered approximately one million Jews from various European countries at Auschwitz II (Auschwitz-Birkenau).