The origin of the "Final Solution," the Nazi plan to exterminate the Jewish people, remains uncertain. What is clear is that the genocide of the Jews was the culmination of a decade of Nazi policy, under the rule of Adolf Hitler. The "Final Solution" was implemented in stages. After the June 1933 Nazi party rise to power, state-enforced racism resulted in anti-Jewish legislation, boycotts, "Aryanization," and finally the "Night of Broken Glass" pogrom, all of which aimed to remove the Jews from German society. After the beginning of World War II, anti-Jewish policy evolved into a comprehensive plan to concentrate and eventually annihilate European Jewry. The Nazis established ghettos in occupied Poland. Polish and western European Jews were deported to these ghettos. During the German invasion of the Soviet Union in 1941, mobile killing squads (Einsatzgruppen) began killing entire Jewish communities. The methods used, mainly shooting or gas vans, were soon regarded as inefficient and as a psychological burden on the killers. After the Wannsee Conference in January 1942, the Nazis began the systematic deportation of Jews from all over Europe to six extermination camps established in former Polish territory -- Chelmno, Belzec, Sobibor, Treblinka, Auschwitz-Birkenau, and Majdanek. Extermination camps were killing centers designed to carry out genocide. Over three million Jews were gassed in extermination camps. In its entirety, the "Final Solution" consisted of gassings, shootings, random acts of terror, disease, and starvation that accounted for the deaths of about six million Jews -- two-thirds of European Jewry.