Final answer:
Eugenics theories most clearly benefited European imperialists, providing justification for their colonial expansionist policies and racial superiority beliefs.
Step-by-step explanation:
Theories of eugenics clearly benefited European imperialists more than the other groups listed. This is because eugenics was aligned with colonial expansionist beliefs, particularly with notions that the colonizers were superior in intelligence and civilization to those they were colonizing. This set of beliefs provided a purported scientific justification for imperial domination and the paternalistic policies enacted by European powers. The movement supported ideas of racial hierarchy that complimented the imperialists' mission to civilize 'lesser' races, a responsibility Rudyard Kipling referred to as 'the White Man's Burden.' Such ideologies were harmful to non-European populations, including immigrant workers who were often the targets of eugenics policies such as forced sterilization — a practice prevalent in the United States in the early twentieth century.