Throughout the late 19th and early 20th centuries, imperialism was justified through the theory of Social Darwinism. This theory sought to apply the theory of biological Darwinism, as proposed by Charles Darwin in "Origin of Species," to human societies. Imperialists justified invading a foreign territory by citing the improvements their culture and innovation had on the occupied territory.
While the theory of Social Darwinism is similar in nature to Darwin's theory of evolution of plants and animals, it was proposed by Herbert Spencer. Spencer is credited with coining the phrase "survival of the fittest" to predict the outcome of imperialism, or the competition between social groups. The first group, the imperial power, maintained more power and resources than the colonized nation. Thus, the cultural and societal characteristics that would distinguish one culture from another were erased, resulting in cultural assimilation.
Social Darwinism is criticized for its exploitation and subjugation of vulnerable populations. It is also believed to have incited racism and xenophobia within imperial nations, as well as influence the decline of the welfare state in the late 20th century. In Marxist thought, Social Darwinism is described as the result of late capitalism and evidence of the decline of civilization.