Megadeath in Mexico

When Hernando Cortés and his Spanish army of fewer than a thousand men stormed into Mexico in 1519, the native population numbered about 22 million. By the end of the century, following a series of devastating epidemics, only 2 million people remained. Even compared with the casualties of the Black Death, the mortality rate was extraordinarily high. Mexican epidemiologist Rodolfo Acuña-Soto refers to it as the time of "megadeath." The toll forever altered the culture of Mesoamerica and branded the Spanish as the worst kind of conquerors, those from foreign lands who kill with their microbes as well as their swords.

The notion that European colonialists brought sickness when they came to the New World was well established by the 16th century. Native populations in the Americas lacked immunities to common European diseases like smallpox, measles, and mumps. Within 20 years of Columbus's arrival, smallpox had wiped out at least half the people of the West Indies and had begun to spread to the South American mainland.

In 1565 a Spanish royal judge who had investigated his country's colony in Mexico wrote:

It is certain that from the day that D. Hernando Cortés, the Marquis del Valle, entered this land, in the seven years, more or less, that he conquered and governed it, the natives suffered many deaths, and many terrible dealings, robberies and oppressions were inflicted on them, taking advantage of their persons and their lands, without order, weight nor measure; . . . the people diminished in great number, as much due to excessive taxes and mistreatment, as to illness and smallpox, such that now a very great and notable fraction of the people are gone. . . .

There seemed little reason to debate the nature of the plague: Even the Spanish admitted that European smallpox was the disease that devastated the conquered Aztec empire. Case closed.

Then, four centuries later, Acuña-Soto improbably decided to reopen the investigation. Some key pieces of information—details that had been sitting, ignored, in the archives—just didn't add up. His studies of ancient documents revealed that the Aztecs were familiar with smallpox, perhaps even before Cortés arrived. They called it zahuatl. Spanish colonists wrote at the time that outbreaks of zahuatl occurred in 1520 and 1531 and, typical of smallpox, lasted about a year. As many as 8 million people died from those outbreaks. But the epidemic that appeared in 1545, followed by another in 1576, seemed to be another disease altogether. The Aztecs called those outbreaks by a separate name, cocolitzli. "For them, cocolitzli was something completely different and far more virulent," Acuña-Soto says. "Cocolitzli brought incomparable devastation that passed readily from one region to the next and killed quickly."

More...