The Worst Epidemic in History? The Scourge of Smallpox in the Americas | History Hit

The Worst Epidemic in History? The Scourge of Smallpox in the Americas

A drawing of smallpox sufferers in the Florentine Codex.
Image Credit: Wikimedia / CC

Smallpox is a virus, passed from person to person primarily through airborne transmission, as well as by touching contaminated objects. With a 30% mortality rate, smallpox was widely, and rightly feared. Those who did survive often suffered serious scarring.

A deadly virus

Originating in farming livestock, the disease crossed over to humans. However, after centuries of exposure, European populations had begun to develop some resistance to the smallpox virus.

However, populations which had not spent the same time in close proximity with farming livestock had no such exposure or resistance. When they were first exposed to such microbes, there was an exceptionally high mortality rate.


Smallpox virus grown in a laboratory. PhD Dre / CC

Why was the Spanish conquest so easy?

Many have wondered precisely why, and how, the Europeans conquered the Americas so swiftly and successfully – Aztec and Inca societies were extremely sophisticated, and although they were not used to horses, or fighting on horseback, they had far greater numbers than the Spanish conquistadors.

In initial skirmishes between Hernan Cortes and Emperor Moctezuma of Tenochtitlan, there is no doubt the Aztecs were naïve about the skill of the invaders they were facing – overconfident, perhaps, because Cortes arrived with only 600 Spaniards. However, after this initial battle they fought with much more strength and tenacity.

Guns and load-bearing animals (I.e. horses) were a considerable advantage for the Spanish, as were the alliances Cortes had made with neighbouring rival city states, but even with these, there is no feasible way they would have been a match for the armies of militaristic Aztec city states.

When smallpox arrived on the shores of Mexico in 1520, it ravaged the population of the Aztec Empire, even killing the emperor.

The stories of the indigenous peoples who made the journey across the Atlantic.
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The psychological effects on the unafflicted cannot be underestimated either – before their very eyes, their families and friends were dying painfully, whilst the Spanish invaders remained seemingly untouched and unaffected.

With no natural resistance, the disease spread rapidly through native populations, devastating the city of Tenochtitlan. It is estimated 40% of the city perished.

Smallpox was not the only new disease to arrive on the shores of America with the conquistadors. Scientists and virologists are still unsure exactly what was behind later epidemics – known as cocoliztli epidemics, but it is thought that the virus was probably of European origin. By the early 17th century, it estimated the native population in Mexico had plummeted from 25 million to around 1.6 million.

Smallpox reached the Inca settlements in Peru long before Francisco Pizarro arrived there in 1526, making his conquest infinitely easier as the disease had killed the emperor, weakening the Inca state as his two sons fought for power.

The Spanish did not have the medical understanding or skill to try and help those afflicted even if they had wanted to, but this does not detract from the fact they were hardly sad to see this happen – some even viewed it as a sign of divine providence.

The worst epidemics in history?

Whilst there have been epidemics with higher overall death tolls in more recent history, the combined death toll of these epidemics in the Americas is thought to have killed roughly 90% of the native population in less than 100 years, making it one of the most deadly outbreaks in history.

Furthermore, it had a huge impact on both Europe and the native populations. Not only was the Spanish conquest made considerably easier by scores of natives being struck down with smallpox, the social and cultural impact of such a large percentage of a population dying had profound effects.

Combined with Spanish attempts to wipe out native religious practices, customs and beliefs, aspects of Aztec, Incan and native culture disappeared in a remarkably short space of time, replaced by a new hybrid culture – Catholicism tinted with vestiages of indigenous cultures.


mexico evangelisation

Page from Historia de la Marina Real Española. Image credit: Biblioteca Rector Machado y Nuñez / CC

Biological warfare

Smallpox, cholera, measles, and other European microbes continued to decimate native populations for several hundred years after the initial conquest. One particularly gruesome rumour suggests that in the mid-18th century, the British infected Native Americans through smallpox-infested blankets in an attempt to wipe out local indigenous populations.

Whether or not this story is completely true remains unclear, but it does illustrate a degree of intentional biological warfare that had not previously been present. Even today, biological warfare remains a highly contentious topic – the 1975 Biological Weapons Convention has outlawed the use of weapons of biological warfare in international law.

Whilst the arrival of new European diseases in the Americas might not have been an intentional or deliberate act, it proved a decisive factor in the conquest and colonisation that followed, and in creating the world as we know it.


The Pyramid of the Sun & the Avenue of the Dead at Teotihuacan. Image credit: Gzzz / CC

Tags: Hernan Cortes

Sarah Roller