The “discovery” of America unleashed horrors. Europeans embarked upon a debauching path of death and destructive exploitation that unleashed murder and greed and slavery. But disease was deadlier than any weapon in the European arsenal. It unleashed death on a scale never before seen in human history. Estimates of the population of pre-Columbian America range wildly. Some argue for as much as 100 million, some as low as 2 million. In 1983, Henry Dobyns put the number at 18 million. Whatever the precise estimates, nearly all scholars tell of the utter devastation wrought by European disease. Dobyns estimated that in the first 130 years following European contact, 95 percent of Native Americans perished. (At its worst, Europe’s Black Death peaked at death rates of 25% to 33%. Nothing else in history rivals the American demographic disaster.) A 10,000 year history of disease crashed upon the New World in an instant. Smallpox, typhus, the bubonic plague, influenza, mumps, measles: pandemics ravaged populations up and down the continents. Wave after wave of disease crashed relentlessly. Disease flung whole communities into chaos. Others it destroyed completely.

Disease was only the most terrible in a cross-hemispheric exchange of violence, culture, trade, and peoples–the so-called “Columbian Exchange”–that followed in Columbus’s wake. Global diets, for instance, were transformed. The America’s calorie-rich crops revolutionized Old World agriculture and spawned a worldwide population boom. Many modern associations between food and geography are but products of the Columbian Exchange: potatoes in Ireland, tomatoes in Italy, chocolate in Switzerland, peppers in Thailand, and citrus in Florida are all manifestations of the new global exchange. Europeans, for their part, introduced their domesticated animals to the New World. Pigs ran rampant through the Americas, transforming the landscape as the spread throughout both continents. Horses spread as well, transforming the Native American cultures who adapted to the newly introduced animal. Partly from trade, partly from the remnants of failed European expeditions, and partly from theft, Indians acquired horses and transformed native American life in the vast North American plains.

The European’s arrival bridged two worlds and ten-thousand years of history separated from each other since the closing of the Bering Strait. Both sides of the world had been transformed. And neither would ever again be the same.

This chapter was edited by Joseph Locke and Ben Wright, with content contributions by with content contributions by L.D. Burnett, Michelle Cassidy, D. Andrew Johnson, Joseph Locke, Ben Wright, and Garrett Wright.