Which theory was a justification for european imperialism

Social Darwinism argues that each nation and people rises and falls as their culture proves its inherent worth or lack thereof. This is proven and demonstrated by the cultural, political, and military expansion of the dominant societies and weakening and elimination of weaker societies. As a result, as Europe was ascendant, it had the right propagate its culture and remove inadequate cultures. Only the fittest societies should survive and it was deemed natural for superior nations to economically and politically dominate less-advanced nations. This policy of dominating less-advanced nations is imperialism.