The Columbian exchange

Before 1492 there were no potatoes in Ireland, no tomatoes in Italy, no chili peppers anywhere in Asia and no horses in the Americas.

A name for a very large swap

In 1972 the historian Alfred W. Crosby published a book called The Columbian Exchange. He argued that the most lasting result of Columbus’s voyages was biological. Long periods of relative isolation helped the Americas develop distinctive plants, animals and disease environments. This was not complete isolation: people and animals had crossed Beringia. After 1492 ships carried living things back and forth across the Atlantic and later the Pacific, on purpose and by accident. Crosby sorted the exchange into three kinds: diseases, animals and plants. His name for it stuck, and his book helped start the field now called environmental history.

Crops that fed the world

The crops of the Americas changed what people ate almost everywhere. Maize and potatoes were especially important. Crosby pointed out that they mattered not only because they are nourishing but because they grow in soils and climates where wheat or rice do poorly: potatoes on cold, wet hillsides and maize in places too dry for rice. Potatoes became a staple across northern Europe, and in Ireland so many poor families came to depend on them that when a disease destroyed the crop in the 1840s about a million people died. Sweet potatoes and maize spread across China. Chili peppers, which were unknown outside the Americas before 1492, became part of the cooking of India, Thailand, Sichuan and Korea. Cassava became a staple food in much of Africa, and tomatoes found their way into Italian food.

Animals and plantations

Horses had lived in the Americas long ago but had died out there about 10,000 years earlier. The Spanish reintroduced horses, and during the 1700s peoples of the Great Plains such as the Comanche and the Lakota had built whole ways of life around hunting bison on horseback. Cattle, pigs and sheep ran wild across the grasslands of Argentina and Mexico. Sugar cane, carried from the Atlantic islands to Brazil and the Caribbean, became the crop that drove the Atlantic slave trade. Coffee, which had come from Ethiopia and Arabia, later turned Brazil into the largest coffee grower in the world. Many of the plantation crops that made Europeans rich were grown in the Americas by enslaved Africans on land taken from Indigenous peoples.

The germs that went west

The most terrible part of the exchange was disease. People in Europe, Africa and Asia had lived for thousands of years among crowded settlements and long-lasting outbreaks, some of them infections that jump from animals to humans (the origin of smallpox itself is uncertain), and survivors had some resistance to smallpox, measles and influenza. The peoples of the Americas had never met these diseases. Smallpox reached Mexico in 1520, in the middle of the Spanish attack on the Aztec empire, and killed a large share of the population of Tenochtitlan. Epidemics often spread ahead of the Europeans themselves, along trade routes between Indigenous towns. Estimates of how many people lived in the Americas in 1492 range from about 8 million to more than 100 million, and so the death toll is uncertain, but historians agree that over the next century the population fell catastrophically, in many regions by well over half. War, forced labour and famine added to the losses from disease.