What led people to criticize Social Darwinism?

Nazism, End of Civil War, Eugenics Failure, The fading of the large embrace of racism and of ideologies like "white man's burden" with the coming of the 20-21st century.

Explanation:

Basically, as humanity advanced it's ethics and morals, ideologies like social darwinism did not stand as strong as they used to. We realized that since humanity is one species, one race of humans cannot be far biologically advanced above another because in order for a race of a species to advance the entire species must advance. UNLESS it is somehow isolated and is forced to evolve above its genre of species. Which was Darwin's point about Finches. However, social Darwinism does not work because Darwinian evolution requires long amount of time or a species that can rapidly evolve. Humans cannot. Also, there is no race of people that have been so far isolated in such a powerfully dangerous enviorment that they rose above the rest of us. EVEN if there was, it most likely would be the people in Africa, not Europe. People realized all these things and started letting go of Racist ideologies like SD.

. political or economical policy that isolates a country from participating in international relationships. it has been suggested that the united states participates in isolationism because of its lack of involvement in particular wars or alliances.