Answer: The theory that was used to justify claims of racial superiority was social Darwinism.
Social Darwinism was a group of ideologies that arose in the late 1800s in which Charles Darwin´s theory of evolution by natural selection, was used to justify certain social views.
According to the theory, the weak were diminished while the strong grew in power over the weak.
One of the persons who adopted social Darwinism was Adolf Hitler, who considered that the German master race had grown weak due to the influence of non-Aryans, so he targeted certain groups of people that he considered biologically inferior for extermination such as jews, homosexuals, etc.
