Disease and the Great Dying

Two worlds kept apart

For thousands of years, the Americas were cut off from Europe, Africa and Asia. Diseases such as smallpox, measles and influenza had developed in the Eastern Hemisphere and had never reached the Americas. So no one there had built up immunity, the body's defense that comes from earlier exposure. Historians call these "virgin soil" epidemics. Surviving one disease gave no protection against the next one to arrive.

Faster than people

When Europeans arrived after 1492, the germs spread quickly. They sometimes moved ahead of the Europeans themselves, carried along existing Indigenous trade routes. Smallpox probably reached the Inca Empire in the 1520s, before Francisco Pizarro did, and epidemics hit parts of North America before sustained contact with Europeans.

1520: the Aztec capital

The earliest documented smallpox outbreak in the Americas was on Hispaniola in 1518. In 1520, smallpox swept through Tenochtitlan, the capital of the Mexica (Aztec) people. It killed many, including the ruler Cuitláhuac. Because so many fell sick at once, few were left to farm or cook, so hunger led to more deaths. The weakened city then faced the Spanish siege of 1521.

Not disease alone

Historians estimate that across the Americas, many regions lost most of their people within about a century. Exact numbers are debated, and estimates vary widely. Some historians and scientists call this collapse the Great Dying. Disease did not act alone: war, enslavement and forced labor, displacement and hunger made the epidemics far deadlier, so immunity alone does not explain the deaths.

Good to know

• Smallpox, measles and influenza had no history in the Americas before 1492, which is why they are called "virgin soil" epidemics.
• The NLM's Native Voices timeline notes that survivors of one disease were still open to the next.
• Some historians, such as David S. Jones, stress that war, enslavement, forced labor, displacement and famine made epidemics far deadlier.
• Tenochtitlan was the capital of the Mexica, often called the Aztecs.
• Estimates of population decline vary by region and are debated; "many regions lost most of their people" stays inside the range historians give.
• "The Great Dying" is used by some historians and scientists for the population collapse of the 1500s; it is not a universal term.

For AP US History learners

This is AP US History Period 1 (1491-1607): know that epidemic disease, together with war and forced labor, caused a steep decline in Native populations after European contact.

Answer to the comment question

Why were these diseases new to the Americas? Because the Americas had been cut off from Europe, Africa and Asia for thousands of years. Smallpox, measles and influenza had developed in the Eastern Hemisphere and had never reached the Americas, so no one there had faced them or built up immunity. That is why historians call these "virgin soil" epidemics.