Battles & Wars › Gunpowder empires › Spanish conquest of the Aztec and Inca empires
Smallpox and Old World epidemics in the Americas
from 1518· Event· Americas
Well documentedSolid records, physical evidence or scientific consensus.
Smallpox, measles and other diseases from Europe and Africa killed a large share of the Americas' Native peoples.
See it on the Battles & Wars map →What happened
Native Americans had no prior exposure to many Eurasian and African diseases. Smallpox reached Hispaniola by late 1518, Mexico in 1520 and the Andes by the late 1520s, often ahead of the Spanish themselves. It killed the Aztec emperor Cuitláhuac and probably the Inca ruler Huayna Capac. Measles, typhus, influenza and later cocoliztli outbreaks followed. With war, forced labor and famine, Native populations fell by an estimated 50–90 percent within a century.
Why it matters
It weakened Native resistance at decisive moments and emptied lands that colonizers then took, shaping the whole later history of the Americas.
How we know
Spanish letters and tribute and census records, Nahua accounts in the Florentine Codex with drawings of the sick, and ancient-DNA studies of burials.
Still debated
Pre-contact population estimates vary enormously, and historians debate how much of the collapse was disease rather than violence and exploitation.
Connections (3)
▸Smallpox and Old World epidemics in the Americas weakened the defenders at Fall of TenochtitlanWell documented
The connection
Smallpox reached Mexico in 1520 with a Spanish force. In late 1520, after the Spanish had been driven out, it swept Tenochtitlan for about two months, killing a large share of its people, including the new emperor Cuitláhuac. When Cortés returned in 1521, the city's leaders, warriors and food supply had been badly weakened.
When and how
Central Mexico, 1520, arriving with Pánfilo de Narváez's expedition, sent to arrest Cortés; Tenochtitlan, autumn 1520.
How we know
The Florentine Codex records Nahua memories of the epidemic, with drawings of the sick, and Spanish accounts note Cuitláhuac's death from the disease.
Debates and open questions
The death rate in the city is unknown, and the tradition blaming a single infected African man in Narváez's force is uncertain.
▸Smallpox and Old World epidemics in the Americas devastated the Aztec and Inca peoples during Spanish conquest of the Aztec and Inca empiresWell documented
The connection
Disease ran ahead of and alongside the conquerors. Smallpox reached the Andes in the 1520s, before Pizarro, probably killing the Inca ruler Huayna Capac and his heir and setting off a civil war between his sons Huáscar and Atahualpa. Repeated epidemics, with war and forced labor, cut Native populations by an estimated 50 to 90 percent within a century.
When and how
Mexico from 1520, the Andes from about 1525–28, and later waves such as Mexico's cocoliztli epidemics of 1545 and 1576.
How we know
Spanish tribute counts and church records show the collapse, Nahua and Andean writers describe the epidemics, and a 2018 ancient-DNA study linked one cocoliztli outbreak to a salmonella fever.
Debates and open questions
Pre-conquest populations, whether Huayna Capac died of smallpox, and the relative weight of disease and colonial violence are all debated.
▸Smallpox and Old World epidemics in the Americas weakened Native nations before and during American Indian WarsWell documented
The connection
Smallpox, measles and other diseases brought by Europeans killed large shares of many Native populations, often before sustained fighting began. In New England an epidemic of 1616–1619 emptied coastal villages just before the Pilgrims arrived. Weakened nations had fewer warriors and less ability to resist settlers in the wars that followed.
When and how
Across North America from the 1500s; New England coast 1616–1619; the 1837 smallpox epidemic among the Mandan and others on the Missouri River.
How we know
Colonial records, missionary and trader reports, Native accounts and winter counts, and studies of skeletons and population data document repeated epidemics.
Debates and open questions
Population figures before contact and death rates are widely debated, as is how often disease was spread on purpose, as was attempted at Fort Pitt in 1763.