Technology & Medicine › Printing & the scientific revolution › Columbian Exchange (crops, animals, diseases)
Epidemics in the Americas
1518–1520 onward (death tolls debated)· Event· Germs, drugs & genetics
Mostly agreedGood evidence; some details, dates or numbers uncertain.
Waves of Old World diseases, above all smallpox, that killed a large share of Native Americans after European contact.
See it on the Technology & Medicine map →How it works
Native Americans had no prior exposure to smallpox, measles, influenza or typhus. Smallpox struck Hispaniola in late 1518 and Mexico in 1520, killing the Aztec ruler Cuitláhuac and weakening Tenochtitlan before the Spanish siege of 1521. It reached the Inca Empire in the 1520s, probably killing the emperor Huayna Capac and setting off a succession war. Estimates vary widely, but within about a century the Native population may have fallen by up to 90 percent, through disease combined with war, enslavement and famine.
Why it mattered
The collapse made Spanish and Portuguese conquest far easier and emptied land that colonists later took. It is among the largest population losses in history.
How we know
Spanish and Indigenous accounts such as the Florentine Codex, colonial tribute and census records, archaeology of abandoned settlements, and ancient DNA from victims.
Still unknown or debated
Pre-contact population estimates range from about 8 million to over 100 million, so the death toll is uncertain; historians also debate how much violence and enslavement, versus germs, caused the losses.
Connections (2)
▸Columbian Exchange (crops, animals, diseases) caused Epidemics in the AmericasWell documented
The connection
Ships from Europe and Africa carried smallpox, measles, influenza, typhus and later malaria and yellow fever. Native Americans, isolated from these diseases for over 10,000 years, had no acquired immunity, and epidemics often spread along trade routes ahead of the conquerors. Disease killed far more people than combat did.
When and how
Beginning on Hispaniola after 1492, with smallpox there in 1518 and in Mexico in 1520, then spreading through Central and South America within a decade.
How we know
Spanish and Indigenous accounts, mission and census records, and ancient DNA from early colonial burials document the diseases and their spread.
Debates and open questions
Which diseases caused some epidemics is unclear; a 2018 DNA study linked Mexico's 1545 'cocoliztli' epidemic to a Salmonella bacterium.
▸Epidemics in the Americas included smallpox, the disease ended by Smallpox eradicationMostly agreed
The connection
Smallpox, which arrived with Spanish ships around 1518–1520, was among the deadliest of the Old World diseases that devastated Native American peoples, alongside measles, influenza and typhus. The same virus kept killing worldwide for another 450 years until the WHO campaign stopped it; the last natural case was in Somalia in 1977.
When and how
Hispaniola in 1518, then Mexico in 1520, where it struck Tenochtitlan during the Spanish conquest; eradicated by a WHO campaign run from 1967 to 1977.
How sure are we?
Spanish and Aztec accounts, including the Florentine Codex, describe the 1520 epidemic; eradication is documented by WHO case records and the 1980 declaration.
Debates and open questions
Death tolls in the Americas are debated, as is the share caused by smallpox versus other diseases, war, famine and enslavement.