Recent outbreaks in the U.S. have drawn attention to the dangers of measles. The Democratic Republic of Congo is fighting a deadly outbreak of Ebola that has killed hundreds.

Epidemics are nothing new, of course. And some widespread infectious diseases have profoundly changed the course of human history.

Five hundred years ago, in February of 1519, the Spaniard Hernán Cortés set sail from Cuba to explore and colonize Aztec civilization in the Mexican interior. Within just two years, Aztec ruler Montezuma was dead, the capital city of Tenochtitlan was captured and Cortés had claimed the Aztec empire for Spain. Spanish weaponry and tactics played a role, but most of the destruction was wrought by epidemics of European diseases.

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