Final answer:
Social Darwinism justified Imperialism by arguing that the conquest of weaker nations by stronger ones was a natural outcome of the 'survival of the fittest'. The theory was popularized by Herbert Spencer and later influenced eugenics.
Step-by-step explanation:
Social Darwinism was a theory that emerged in the Victorian era, heavily influenced by a misinterpretation of Charles Darwin's theory of evolution. It proposed that human societal advancement would be attained by ensuring that only the 'fittest' individuals survived and thrived within the community. The principle was prominently applied to justify certain practices and ideologies during that period.
Among the options provided, Social Darwinism was used to justify Imperialism. It was employed by some to argue that the conquest and domination of weaker nations by stronger ones was a natural and beneficial outcome of the survival of the fittest. This rationale was particularly popular during the times of colonial expansion where European powers sought to extend their dominance over various parts of the world.
Herbert Spencer, a British sociologist, was a notable advocate of this idea and is often associated with the term 'survival of the fittest'. This ideology also paved the way for eugenics, which sought to 'improve' the human population through selective breeding and other methods aimed at reducing the reproduction of people deemed 'unfit'.