The Eradication of Smallpox
Smallpox killed perhaps 300 million people in the twentieth century alone and had been killing for at least three thousand years. A global campaign — run through the Cold War with Soviet and American cooperation, using ring vaccination to surround each outbreak rather than trying to vaccinate everyone — chased it down to its last cases in Somalia in 1977. In 1980 the World Health Organization declared it gone. It is the only human disease ever deliberately driven to extinction, and the virus now exists in two freezers.
A pathogen spreads through a population and reshapes its demography, economy, and beliefs at once.