Ferguson dedicates the fourth chapter to the development of medicine. He links the pursuit of medical research in the West to imperialist exploits abroad, especially in 19th- and early 20th-century Africa, the pseudo-science of eugenics, and World War I. He suggests that colonial subjects received the benefits of civilization in the form of cutting-edge medical treatment. On the other hand, the colonizers subjected the local populations in Africa to forced labor, and concentration camps, and used them as cannon fodder in World War I. 

The zenith of Western empires was between the middle of the 19th and the middle of the 20th centuries when “the West ruled over the Rest” (142). Countries comprising “10% of the world’s land surface governed more than half the world” (144). Empire took on different forms, and domination of others was both formal and informal. It was a “living space for surplus population,” a way to mitigate conflicts and engage in “civilizing” pursuits like missionary work (142). Of all European empires, Britain was the largest, whereas Germany was late in the game.

The global life expectancy between the early 19th and early 21st centuries rose from 29 to 67 years.