Imperialism involved the domination of one nation over another through unequal economic and political relationships, usually in the form of colonies or empires. Key aspects included colonialism, where one territory established control over another, and annexation, where a smaller territory was incorporated into a larger one. Imperialist thinking in the late 19th century was influenced by Social Darwinism and ideas of racial superiority that justified the expansion and domination of stronger Western nations over weaker non-Western nations.