8.5 — The Americas Conquered, and the Columbian Exchange

Hernán Cortés landed in Mexico in 1519 with about 500 men, 16 horses and 14 cannon. Two years later the Aztec empire, with a capital of some 200,000 people and a tributary population in the millions, no longer existed.

Francisco Pizarro reached Peru in 1532 with about 168 men. Within a year he had captured the Inca emperor and effectively controlled an empire of some 10 million people spread over 4,000 kilometres.

The standard explanation is guns, horses and steel. That explanation is a small part of the answer. This chapter gives the rest.

What actually explains the conquest

1. Disease, first and largest

Chapter 3.8 established the mechanism. The Americas had almost no domesticated herd animals, therefore no reservoir for crowd diseases, therefore no exposure and no acquired resistance to smallpox, measles, typhus, influenza and the rest.

Smallpox reached the Aztec capital in 1520, during the war, brought by a member of a Spanish expedition. It killed a large fraction of the city's population, including the emperor Cuitláhuac, over the following months. Cortés's final siege was against a city already devastated by an epidemic.

Smallpox reached the Inca empire ahead of Pizarro, travelling overland from Central America. It killed the emperor Huayna Capac and his designated heir, which triggered a civil war between his sons Atahualpa and Huáscar. Pizarro arrived at the end of that war, into an empire that had just torn itself apart.

The timing in both cases is not coincidental to the outcome; it is most of the outcome.

2. Indigenous allies

Cortés did not conquer Mexico with 500 Spaniards. He conquered it with tens of thousands of indigenous troops.

The Aztec empire ran on tribute and on wars fought partly to obtain captives (Chapter 4.5), and its subject peoples hated it. Tlaxcala, an independent state that had resisted the Aztecs for generations, allied with Cortés and supplied the bulk of his army. Other tributary cities defected as the campaign advanced.

From the Tlaxcalan point of view this was not a foreign conquest of Mexico. It was a coalition war against a hated hegemon, in which they were the main force and the Spaniards were useful allies with unusual equipment. They spent the next two centuries petitioning the Spanish crown for the privileges they believed they had been promised.

The same pattern in Peru: Pizarro allied with the faction that had lost the civil war, and with subject peoples resentful of Inca rule.

3. Decapitation

Both empires were highly centralised with divine or semi-divine rulers. Seize the ruler and the command structure stops.

Pizarro captured Atahualpa at Cajamarca by inviting him to a meeting and ambushing his unarmed retinue. He then collected an enormous ransom in gold and silver and executed him anyway.

A decentralised society is far harder to conquer this way, which is why the northern Mexican and North American peoples, and the Mapuche in Chile, resisted for centuries — the Mapuche were never conquered by Spain and negotiated a recognised frontier.

4. Then the technology

Steel armour and swords were genuinely superior to obsidian-edged weapons, which cut terribly and shatter against metal.

Horses were decisive in open terrain and useless in mountains and forests.

Firearms of the period were slow, unreliable and few — their psychological effect on first contact exceeded their tactical value, and it faded fast.

Ships and the ability to reinforce across an ocean mattered more than any battlefield weapon.

The honest ordering: disease, then indigenous allies and internal division, then decapitation, then technology. The popular account inverts it.

The demographic catastrophe

Estimates of the pre-contact population of the Americas range from about 40 million to over 100 million, and the range reflects genuine uncertainty in method.

The decline over the following 150 years is estimated at somewhere between 50 and 90 percent depending on region, with some Caribbean island populations effectively eliminated.

The great majority of the deaths were from disease, which arrived ahead of Europeans in many regions and killed people who never saw one.

And the rest was killing, forced labour and social collapse. The encomienda granted Spanish settlers the labour of indigenous communities in exchange for a nominal obligation to Christianise and protect them; in practice it was forced labour, and mortality in the silver mines at Potosí and the mercury mines at Huancavelica was extreme. The mita labour draft, adapted from the Inca system, sent rotating conscripts to those mines.

Bartolomé de las Casas, a Dominican friar who had himself been an encomendero, spent decades documenting and denouncing the treatment of indigenous people and campaigning at the Spanish court. The Valladolid debate of 1550–51, in which he argued against Juan Ginés de Sepúlveda over whether indigenous Americans were natural slaves, is one of the earliest formal debates anywhere about the rights of conquered peoples. Las Casas won the argument in the sense that the crown issued laws restricting the encomienda, and lost it in the sense that the laws were widely ignored.

And there is a genuinely striking climate finding attached to this. The collapse of American agriculture — tens of millions of hectares of farmland reverting to forest as farmers died — pulled enough carbon dioxide out of the atmosphere to be measurable in Antarctic ice cores, and it is one proposed contributor to the coldest phase of the Little Ice Age around 1610. The proposal is debated and the ice-core signal is real. It is the clearest illustration in this volume that human population change can register in the planet's chemistry.

The Columbian Exchange

The term is Alfred Crosby's, and the biological exchange changed what every human being on Earth eats.

From the Americas to the world

Crop	Where it mattered most
Potato	Northern Europe, Ireland, later India and China
Maize	Africa, southern Europe, China
Cassava	West and Central Africa
Sweet potato	China, Japan, Pacific
Tomato	Italy, Mediterranean
Chilli	India, Southeast Asia, China, Korea
Cacao, vanilla	Europe and everywhere
Tobacco	Everywhere, with the health consequences
Rubber, quinine	Industrial and medical, later

Potatoes and maize matter demographically. A hectare of potatoes yields far more calories than a hectare of grain on the same land, they grow on poor soil, and they are underground and therefore harder for an army to burn. The adoption of the potato in northern Europe is associated with substantial population growth, and economic historians have estimated it accounts for a meaningful share of Old World population and urbanisation increase after 1700.

Maize and cassava did the same in Africa, and — this is the uncomfortable connection — the population growth they supported partly offset the demographic drain of the slave trade, which is a factor in why the trade could continue at the scale it did.

Sweet potato and maize in China allowed cultivation of hilly and marginal land, and Chinese population roughly tripled between 1700 and 1850.

And the nutritional catch from Chapter 4.5 applies. Maize adopted without nixtamalization produced pellagra epidemics in Italy, Egypt, and the American South well into the twentieth century.

From the world to the Americas

Wheat, rice, sugarcane, coffee, bananas, citrus — and sugar above all, which is the crop that drives Chapter 8.6.

Horses, cattle, pigs, sheep, goats and chickens. Horses transformed the North American plains, where peoples who had hunted bison on foot became mounted societies within a few generations — the Comanche, Lakota and Cheyenne cultures of the popular imagination are a post-contact development built on a European animal.

Cattle and pigs multiplied enormously in the absence of predators and competitors and transformed landscapes, in many places destroying indigenous agriculture by trampling and grazing.

And the diseases, as above. Syphilis is the possible reverse traffic — an epidemic began in Europe in the 1490s, and the American-origin hypothesis has real evidence and remains contested.

Silver, and the first global economy

The mountain at Potosí, in what is now Bolivia, discovered in 1545, produced silver on a scale that changed the world's money.

The scale. Potosí was one of the largest cities in the world by the early seventeenth century — comparable to London or Paris — at 4,000 metres altitude, populated by conscripted indigenous labour and enslaved Africans, with mortality that contemporaries described as devouring men.

Where the silver went is the interesting part. China had converted its tax system to silver payment and had an enormous demand for it, so silver was worth substantially more in China than in Europe. A merchant could buy silk and porcelain in China with silver at a large profit.

So American silver flowed to China, by two routes: west across the Atlantic to Spain and then east through Europe and the Indian Ocean, and directly across the Pacific on the Manila galleon, which ran annually from Acapulco to Manila from 1565 for 250 years.

This is the world's first genuinely global trade circuit, and it is why economic historians date the beginning of globalisation to the sixteenth century rather than the nineteenth.

And it produced Europe's first great inflation. The Price Revolution — a roughly sixfold rise in European prices over the sixteenth century — is conventionally attributed to the silver influx, and modern work adds population growth and debasement as contributors. Chapter 9.8 uses it.

Spain itself got poorer in relative terms, which is the resource-curse pattern of Chapter 1.12 appearing early: the crown spent the silver on wars, defaulted repeatedly despite the income, and Spanish manufacturing was undercut by imports that the silver made affordable. The Dutch and English, who had no silver, built the industries and the financial institutions.

Where this shows up in your life

Your plate. Chapter 4.5 listed it and it bears repeating: Italian food without tomatoes, Indian food without chillies or potatoes, Swiss chocolate, Belgian chips, Thai and Korean cooking without chillies — none of it existed before 1492. The cuisines that feel most timelessly national are, in most cases, under five hundred years old.

The world's languages and religions in the Americas.

And a question this volume keeps returning to. The conquest was not a demonstration that one civilisation was superior to another. It was the meeting of two biologically isolated populations, one of which had spent ten thousand years living beside domesticated herd animals and had the immune history to show for it. Chapter 4.5 said that the absence of about a dozen wild species from two continents accounts for most of the difference, and this chapter is where that fact cashed out in human lives.

What the next page covers

Sugar was the most profitable crop in the world and it required enormous quantities of labour in a climate that killed the workforce. Chapter 8.6 covers the Atlantic slave trade in full — the numbers, sourced; how the trade actually worked at each end; the economics that drove it; what the Middle Passage was; the resistance and the revolts; how abolition happened and why; and the honest accounting of who profited, who participated, and what the consequences were for Africa, the Americas and Europe.