Smallpox Kills Thousands of Indigenous Americans

The devastation wrought upon the Aztec Empire and other American Indian cultures left them unable to defend themselves against the Europeans. The resulting defeat and subjugation of the Aztec Empire by Hernán Cortés opened the way to Spanish domination of Mexico and much of western North America.

Summary of Event

On April 21, 1519, eleven Spanish ships under the command of the Spanish adventurer Hernán Cortés weighed anchor on the east coast of what would become Mexico. On the ships were some 550 soldiers and sailors. The goal of the expedition was to establish a Spanish presence in the area and discover gold or other treasures for their king, Charles I (Holy Roman Emperor Charles V). In addition, the Spanish hoped to convert the Central American Indians to Christianity, the dominant religion of Spain. Meeting Cortés were representatives of the Totonacs. The land was claimed on behalf of the Spanish king, and Cortés prepared to travel inland. Exploration and colonization;Spain of North America
Smallpox;in the Americas[Americas]
Native Americans;smallpox and
Cortés, Hernán
Montezuma II
Alvarado, Pedro de
Velázquez, Diego
Narváez, Pánfilo de
Cortés, Hernán
Montezuma II
Velázquez de Cuéllar, Diego
Narváez, Pánfilo de
Alvarado, Pedro de

For Europe, the early sixteenth century was a time of discovery in the New World, with Spain and Portugal in the forefront of European exploration. During the second decade of the century, several Spanish explorers had already probed the gulf coast region in the area of the Yucatán Peninsula, with limited success. The 1519 expedition led by Cortés represented only the newest attempt to establish a Spanish presence on the mainland.

Cortés’s landing came as no surprise to Montezuma II, the ruler of the Aztec (Mexica) Empire Aztec Empire . Runners had brought word to the capital of the Spanish landing. Legend suggests that the Aztecs mistook Cortés for Quetzalcóatl, Quetzalcóatl (Aztec god) a light-skinned god who it was believed would appear in the east, and who would ultimately rule over the empire. The reality of the situation is less clear. Montezuma had been selected as ruler in 1502 by a council of nobles. He was a youthful and brilliant warrior, dominating his enemies in a large region around the capital. He was, as well, an enlightened ruler, and, as a student of Aztec theology, was certainly aware of the Quetzalcóatl legend.

There exists little evidence, however, that Montezuma subscribed to the legend of Quetzalcóatl, and in all likelihood, the story was a myth developed by Franciscans Franciscans;Aztec Empire for their own theological purposes. The reaction of the Aztecs to the Spaniards was directed more toward the latter’s weaponry and the horses they were riding, neither of which the Aztecs had ever encountered before. It is clear, however, that Montezuma initially welcomed Cortés, allowing the Spanish to enter the capital of Tenochtitlán as well as the royal palace. In response, Cortés took Montezuma captive.

The origin of the smallpox epidemic is obscure. Given the disease’s relatively short incubation period (one to two weeks), it is unlikely that Cortés brought the virus with him on the ships. Furthermore, no written record from the conquest provides any evidence that Cortés’s crew carried the virus. However, the endemic nature of the disease in Spain would probably have resulted in immunity among the crew by this time.

Historian William Prescott has suggested another possible source for the virus: a slave belonging to Diego Velázquez de Cuéllar, the Spanish governor of Cuba. If true, this theory reveals an irony to Cortés’s eventual conquest. Velázquez was resentful of Cortés’s success in the initial stages of his invasion of the Americas and was particularly jealous of the treasures Cortés had obtained. As a result, Velázquez decided to assert his own authority and arranged for a naval force consisting of some eighteen ships, nine hundred soldiers, and approximately one thousand slaves and local natives under the authority of Pánfilo de Narváez. Their objective was to occupy Mexico in place of Cortés. Cortés, however, became aware of the Velázquez expedition and moved against him first. Leaving the Tenochtitlán garrison under the command of Pedro de Alvarado and extracting a promise of neutrality from the captive Montezuma, Cortés overran the enemy camp and captured Narváez. Cortés ensured the loyalty of Narváez’s men by bribing them with the Aztec gold.

The source of the smallpox virus in all likelihood was the invasion force under Narváez. Among the enslaved members of that force may have been a person with smallpox, then endemic in Cuba. The first outbreak among the indigenous population occurred at the landing area of Cempoalla. In response to the high fever symptomatic of the disease, the Indians would bathe in cold water, a practice that served only to exacerbate the illness. The smallpox epidemic spread over the entire area, reaching the capital of Tenochtitlán later that year. Among its later victims was Cuitláhuac, Montezuma’s successor as ruler.

In Cortés’s absence, de Alvarado mistook a religious celebration by the Aztecs for a rebellion, and his response resulted in the slaughter of thousands of Aztecs, which transformed their uprising from an imagined revolt into a real one. Montezuma, attempting to calm his subjects, was seriously injured by a rock thrown at his head, and he died several days later. He was succeeded by his brother Cuitláhuac.

There is significant disagreement over the precise population of the Aztec Empire in 1519, but the most reliable figures suggest it was approximately 5 million. The population of the capital, Tenochtitlán, appears to have been approximately 300,000. Following his defeat of the expedition under Narváez, Cortés and some five hundred soldiers returned to Tenochtitlán. His forces were supplemented by around twenty-five thousand to fifty thousand warriors, principally from native tribes previously subjugated by the Aztecs. After building a causeway to allow access by his ships carrying supplies and ammunition, Cortés set siege to the capital.

Somehow, smallpox entered the city. It had spread from the coast, through the countryside of Tlascala, and into the capital. Among its first victims was Cuitláhuac. From Tenochtitlán, the epidemic spread to the Pacific coast and south through Central and South America. In its path, unknown numbers died; the estimate among the Franciscans was that millions ultimately perished. Within a generation, the population of much of the Americas had been reduced by 90 percent.

When Cortés entered the city, the streets were described as being so filled with the dying and dead that the “men could walk over nothing but bodies.” The Aztecs, now under the leadership of Cuauhtémoc, continued to resist the Spanish. Even with European weapons and native allies, there is legitimate question as to whether Cortés could ultimately have been successful in the absence of the disease. Smallpox had so ravaged the Aztec population, however, that both the means and the will to resist had disappeared. On August 13, 1521, Cuauhtémoc surrendered to Cortés.


The introduction of smallpox in 1519 during the conquest by Cortés decimated the indigenous population, enabling the Spanish to conquer the North American Indians by 1521 and to establish colonies in what would become the southwestern United States and Mexico. This would not be the only time the pestilence would be introduced into parts of the Americas from Europe, and the staggering effects of disease on a population lacking any previous exposure would be repeated through numerous epidemics covering the next three centuries.

The population of the Aztecs at the time of the Cortés expedition is unknown, but it probably numbered in the millions. The deaths en masse of the natives produced two significant effects, one practical and the other psychological. First, Cortés accomplished his mission of conquering the native peoples with a relative handful of men. Even given the presence of weapons viewed as devastating by the natives, the ability of such small numbers to be victorious required additional factors. There is no question that elimination of most of the opposition through disease opened the way for Spanish conquest. In addition, the rapid decimation appeared to some of the natives as an indication the gods were on the side of the conquerors. Psychologically, the Aztecs were forced to conclude that Cortés could not be resisted.

Further Reading

  • Crosby, Alfred. Ecological Imperialism: The Biological Expansion of Europe, 900-1900. New York: Cambridge University Press, 1993. Explores the role of disease in the conquest of lands by European powers. Included are descriptions of the effects on the Aztec population of the Americas.
  • Díaz del Castillo, Bernal. The Discovery and Conquest of Mexico. Translated by A. P. Maudslay and edited by Genaro García. New York: DaCapo Press, 2004. Account of Cortés’s conquest of Mexico by a conquistador who accompanied him.
  • Fenn, Elizabeth. Pox Americana. New York: Hill and Wang, 2001. A description of the smallpox epidemics that devastated populations, both native and newly arrived, in the Americas during the late eighteenth century.
  • Fenner, Frank. Smallpox and Its Eradication. Geneva: World Health Organization, 1988. Primarily a history of the disease. The author does address the effects of smallpox on populations that had no natural immunity.
  • Prescott, William H. History of the Conquest of Peru. London: Phoenix Press, 2002. Part of Prescott’s classic series on the conquest of the Americas by Spain.
  • Prescott, William H. The World of the Aztecs. Barcelona, Spain: Industria Grafica, 1974. Reprint of Prescott’s classic account (1843) of the defeat of the Aztecs. Prescott, grandson of the American commander at Bunker Hill, became a noted Spanish historian.
  • Restall, Matthew. Seven Myths of the Spanish Conquest. New York: Oxford University Press, 2003. The author provides a new perspective on the Spanish conquest of the Americas. Argues, for example, that the native perception of the conquest was that of a civil war, rather than a foreign invasion.

Oct. 12, 1492: Columbus Lands in the Americas

1493-1521: Ponce de León’s Voyages

1500-1530’s: Portugal Begins to Colonize Brazil

1502-1520: Reign of Montezuma II

Apr., 1519-Aug., 1521: Cortés Conquers Aztecs in Mexico

Aug., 1523: Franciscan Missionaries Arrive in Mexico

1527-1547: Maya Resist Spanish Incursions in Yucatán

1528-1536: Narváez’s and Cabeza de Vaca’s Expeditions

1532-1537: Pizarro Conquers the Incas in Peru

1545-1548: Silver Is Discovered in Spanish America

1552: Las Casas Publishes The Tears of the Indians