The 1 million figure quoted in the figure only relates to the use of Zyklon B at the gas chambers installed at Auschwitz-Birkenau, Majdanek, and other extermination camps. Einsatzgruppen killed over 2 million people, including some 1.3 million Jews, gas vans (using gasses other than Zyklon B) were used to murder large numbers, while many others were worked to death or simply died as a result of hunger and disease.
A breakdown of how and where victims of the Holocaust and Nazi Persecution died can be found on the United States Holocaust Memorial Museum website. It doesn't make for easy reading. The following breakdown of Jewish deaths in the Holocaust is taken from there.
- Auschwitz complex (including Birkenau, Monowitz, and subcamps):
approximately 1 million
- Treblinka 2: approximately 925,000
- Belzec: 434,508
- Sobibor: at least 167,000
- Chelmno: 156,000–172,000
- Shooting operations at various locations in central and southern
German-occupied Poland (the so-called Government General): at least
- Shooting operations in German-annexed western Poland (District
Wartheland): at least 20,000
- Deaths in other facilities that the Germans designated as
concentration camps: at least 150,000
- Shooting operations and gas wagons at hundreds of locations in the
German-occupied Soviet Union: at least 1.3 million
- Shooting operations in the Soviet Union (German, Austrian, Czech Jews
deported to the Soviet Union): approximately 55,000
- Shooting operations and gas wagons in Serbia: at least 15,088
- Shot or tortured to death in Croatia under the Ustaša regime:
- Deaths in ghettos: at least 800,000
- Other*: at least 500,000
*"Other" includes, for example, persons killed in shooting operations in Poland in 1939–1940; as partisans in Yugoslavia, Greece, Italy, France or Belgium; in labor battalions in Hungary; during antisemitic actions in Germany and Austria before the war; by the Iron Guard in Romania, 1940–1941; and on evacuation marches from concentration camps and labor camps in the last six months of World War II. It also includes people caught in hiding and killed in Poland, Serbia, and elsewhere in German-occupied Europe.