Genocide
The term genocide
was legally defined only in 1948, when the United Nations adopted its genocide convention (see www.un.org/en/genocide-prevention/1948-convention). According to this convention, genocide does not require the mass murder of members of a defined group because they belong to that group. Already any measure that causes serious bodily or mental harm, deliberately creates conditions leading to death, or prevents the ability of a defined group to procreate is seen as genocide, if these acts or committed with the intention to target a specific group of people.
Between early 1942 and late 1944, it was National-Socialist policy to deport Jews — because they were Jews — from many European countries to camps, where the genders had to live and work separated from each other. Hence, these Jews were deliberately put in a position where they could not procreate. Furthermore, Jews in German-created and controlled camps and ghettos were subjected to conditions that inevitably had to lead to serious bodily and mental harm, and to the death of many, just because they were Jews.
Therefore, if we use the 1948 UN definition of genocide, those responsible for defining and implementing this National-Socialist policy did indeed commit genocide against the Jews, even if there were no mass executions by gas vans, gas chambers or shootings. While it is true that those legally responsible for these acts could not have been prosecuted under this 1948 convention, they are still burdened with moral responsibility.
Genocide
and gas chamber
are two separate issues that should not be conflated. We need to keep in mind that the history of mankind is unfortunately full of other genocides. None of these required gas chambers to be perpetrated. For instance, the Allied policy toward Germans during and after WWII also qualifies as a genocide, with no gas chambers present. Hence, the question whether or not the Third Reich employed homicidal gas chambers to murder Jews has no connection to the question of whether there was a genocide.