The Biology of the Second Reich: Social Darwinism and the Origins of World War I
Social Darwinism is the attempt to apply biological principles such as "survival of the fittest" to societies (e.g., the social and political realms). The results may include racism ("race X is more highly evolved than race Y, so race X is superior"), eugenics ("improving" the human gene pool by selective breeding and sterilizations), and war ("inferior societies should be crushed to make room for superior societies"). Social Darwinists may also maintain that compassion for the weak or sick is detrimental to civilization (because the sick and the weak would have been eliminated by natural selection, and preserving them contrary to nature will therefore stunt the development of humanity).
The following video suggests that social Darwinism provided a kind of intellectual justification for World War I (as it certainly did for World War II).