Following Christopher Columbus's 1492 voyage, a sustained transfer of crops, animals, people, technologies and diseases began between the Americas, Europe and Africa across the Atlantic. The Americas gained wheat, horses, cattle and sugar, while maize, potatoes, tomatoes and cacao spread to the Old World, transforming diets and agriculture. Most devastatingly, Old World diseases such as smallpox and measles, to which Indigenous Americans had no immunity, caused epidemics that killed up to roughly 90 per cent of some populations. The exchange also drove the transatlantic slave trade.
It collapsed Indigenous settlement systems through catastrophic depopulation and recast agriculture worldwide, altering which lands could feed populations and so where cities could be sustained on both sides of the Atlantic.