Einsatzgruppen were paramilitary groups formed by Heinrich Himmler and operated by the SS before and during World War II. The Einsatzgruppen had among their tasks the murder of those perceived to be racial or political enemies found behind German combat lines. The Einsatzgruppen killed more than one million Jews, almost all civilians, beginning with the Polish and then quickly progressing, by 1941, to primarily killing the Jews of Eastern Europe. After time, it was found that the killing methods used by the Einsatzgruppen were inefficient because it did not kill the victims quickly enough. At the Wannsee Conference, SS and various other officials met to find a more efficient way of killing their victims; this ultimately led to the establishment of extermination camps containing gas chambers. Also the production of Zyklon B was introduced.
Between 1933 and 1945, Nazi Germany established about 20,000 camps to imprison its many millions of victims. These camps were used mainly for mass murder. The Auschwitz concentration camp complex was the largest of its kind established by the Nazi regime. It included three main camps, all of which arranged prisoners at forced labour. The first death camp began gassing Jews was at Chelmno, Poland. It was the first extermination camp, opened in 1941 to kill the Jews of the Łódź Ghetto and the Warthegau. At least 153,000 people were killed in the camp, mainly Poles and Jews from the Łódź Ghetto and the surrounding area.
The Nazis established killing centers for efficient mass murder. Unlike concentration camps, which served primarily as detention and labor centers, killing centers were almost entirely "death factories." German SS and police murdered nearly 2,700,000 Jews in the killing centers either by asphyxiation with poison gas or by shooting. Mostly Jews, but also Roma (Gypsies), were gassed in mobile gas vans there. Almost all of the deportees who arrived at the camps were murdered in the gas chambers. Jews were transported to these camps by train being packed to capacity. The largest killing center was Auschwitz Birkenau, which by spring 1943 had four gas chambers (using Zyklon B poison gas) in operation. They used it by throwing pellets of it through small holes of the Gas chamber. Victims corpses were cremated or either buried in mass graves.
The Final Solution was Nazi Germany's plan and execution of its genocide against European Jewry during World War II, resulting in the final, most deadly phase of the Holocaust. Hitler termed it: "the final solution of the Jewish question. Mass killings of about one million Jews occurred before the plans of the Final Solution were fully implemented in 1942. This decision to systematically kill the Jews of Europe was made by the time of the Wannsee conference, which took place in Berlin, in the Wannsee Villa on January 20, 1942. During the conference, there was a discussion held by a group of German Nazi officials to decide on the "Final Solution of the Jewish Question.
