Which development stemmed from the popularity of social darwinism and eugenics in the early twentieth century?

Answer: Restriction on immigration increased.

Explanation:

Eugenics was a popular movement to control human breeding that blossomed in the first half of the twentieth century. It was based on the assumption that differences in human mentality, character, and temperament and composure were greatly due to differences in heredity, and this drove the fear that the individuals whose heredity was poor were more prolific than those of good conformation.

Social Darwinism theory opined that human groups and races are subject to the same laws of natural selection as Charles Darwin perceived in plants and animals in nature.

The pernicious beliefs of Social Darwinism shaped Americans' relationship with peoples of other races and countries. Many whites believed that the new immigrants, who were from Eastern or Southern Europe, were racially inferior and consequently "less evolved" than immigrants from England, Ireland, or Germany which led to an increase in restriction on immigration.

During and after World War II, the ideas of Social Darwinists and eugenicists lost popularity in the United States due to their association with Nazi racial propaganda.