When the continents began to trade

An old black-and-white engraving depicts the mountain of Potosí. — Potosí: drawing from the Chronicle of Peru, published in 1553. A.Skromnitsky, Public domain, source

It is often said that in 1492 a navigator discovered America.

The word “discover” deserves a closer look. One discovers a desert island, a cave, a star. One does not discover a place where people live.

Two worlds separated for millennia

To understand what happened after 1492, we need to gauge what existed before.

The Americas were peopled at least fifteen thousand years ago by groups who came from North-East Asia. Then sea levels rose, the passage closed, and the two halves of the world developed separately for millennia. Each developed its own plants, its own domestic animals, its own diseases and its own civilisations — the Maya, the Aztecs, the Incas, and hundreds of other societies.

This separation explains everything that follows. When the two worlds were abruptly reconnected, each brought the other what it had never encountered. Historians call this movement the Columbian exchange, after Christopher Columbus.¹

It was made up of three flows, and they did not carry the same weight.

Plants. Maize, the potato, the tomato, the bean, cacao, chilli pepper and tobacco left the Americas; wheat, rice and sugar cane arrived there. This transfer brought a lasting increase in the amount of food available throughout the world.
Animals. The horse, the cow, the sheep and the pig arrived on a continent that had almost no large domestic animals — which overturned ways of travelling, farming and making war.
Diseases. And this was the heaviest flow, almost one-way. Smallpox, measles and typhus, familiar in Europe, were unknown in the Americas. The populations there had no immunity, and they collapsed.²

Why one-way? The answer lies in the animals. Most of these diseases came from European farm animals, to which the inhabitants of the Americas had never been exposed. Influenza, smallpox, plague and others ravaged the Americas — and not vice versa.³

The Americas had almost no large domestic animals — the llama, the alpaca, the dog, the guinea pig and a few kinds of poultry, nothing comparable to the oxen, pigs, sheep and horses of Eurasia. No herds, therefore none of these diseases, therefore no immunity when they arrived all at once.

The two flows — animals and diseases — are therefore the same fact, seen from two sides.

This asymmetry is essential, because the rest of this page depends on it: the exchange was reciprocal for plants, but not for diseases. It is this imbalance, and not military superiority, that explains most of what happened.

How many people?

Researchers gathered one hundred and nineteen published estimates and derived a number from them: before 1492, the Americas had about sixty million inhabitants.⁴

This number is a midpoint, not a certainty: the middle half of the estimates ranges from forty-five to seventy-eight million. What matters is the order of magnitude, not the decimal place.⁵

So there was nothing to discover. There was an encounter between two halves of the world that knew nothing of each other.

What happened next

In less than a hundred years, epidemics from Europe carried off 90% of this population.⁶

Nine people in ten: researchers call this the Great Dying.

🦠 The causes of the decline:
Diseases from Europe (smallpox, measles, influenza) to which no one was immune: the bulk of the deaths.
War, forced labour and the destruction of crops: the rest.

To give a sense of scale, each of these diseases on its own killed about three people in ten — the order of magnitude of the Black Death in Europe. What happened in the Americas was a series of these epidemics in rapid succession, with no respite between them.⁷

A lesson about numbers

It remains to ask where this figure of “sixty million” comes from, because its origin is a lesson for this whole encyclopaedia.

Depending on the author, figures ranging from eight million to more than a hundred million have been proposed for the population before 1492.⁸

One example shows the scale of the problem. For a single Caribbean island, a sixteenth-century witness claimed four million inhabitants; a census taken in 1508, eleven years after the first epidemic, counted sixty thousand. If the first figure is believed, almost the entire population vanished; if not, the fall can no longer be measured.⁹

Why such a gap?

The technical difficulty: A population has to be reconstructed without a census, from excavations, accounts and traces of fields.
The historical bias: The earliest historians, who wrote from Europe, gave the lowest figures. A low figure makes the conquest smaller.

💡 Key question: It applies to every page of history: who produced this figure, and in what context?

An important clarification, to avoid a mistaken conclusion: the uncertainty concerns the count, not what happened. That researchers debate an order of magnitude does not mean that they debate the fact.

An effect no one expected

🧪 Scientific hypothesis:
Sixty million people farmed fields — a little over a hectare each. When they disappeared, the fields were abandoned and the forest grew back. And a growing forest absorbs carbon.¹⁰

The team that made this calculation estimates that nearly fifty-six million hectares were thus reclaimed by vegetation, and that the carbon absorbed, with its knock-on effects, accounts for between half and two thirds of:¹¹

A fall in carbon dioxide in the atmosphere in the late 1500s and early 1600s;
A slight cooling of the planet — about 0.15 °C;

If this is correct, humans altered the Earth’s climate before the Industrial Revolution. They did so by dying.

This is the thesis of one team, published in a scientific journal and discussed by other researchers. Other studies, focusing on Amazonia, find no synchronous forest regrowth at that date. It is therefore not established.¹²

Follow the silver

Then comes the question that is almost never asked: what were all these ships for?

In the middle of the sixteenth century, silver was found in a mountain in the Andes, more than four thousand metres above sea level: the Cerro Rico. The town that sprang up at its foot is called Potosí.

Within a few decades, it grew from about fourteen thousand inhabitants to more than a hundred thousand — one of the most populous cities in the world at the time, larger than most cities in Europe.¹³

The underestimated destination

Between 1500 and 1800, Spanish America, with the Cerro Rico of Potosí and the mines of Mexico, produced about 80% of the world’s silver. What almost no one mentions: a very large share of this silver did not stay in Europe. It ended up in Asia, and above all in China.¹⁴

Estimates range from a third to about half depending on the author, and the silver reached it by two paths, not just one. The more spectacular was the Manila galleon, which crossed the Pacific from Acapulco from 1565 onwards: this was the direct route, and it carried something of the order of twenty to thirty thousand tonnes. But the bulk of the metal first passed through Europe, before setting off again for Asia via the Cape.¹⁵

In 1581, the Ming dynasty rolled out across the empire a fiscal reform known as the “Single Whip Law”: taxes — the land tax in some regions, corvée labour in others — were now paid in money rather than in kind, that is, in silver. A vast empire thus began to demand it, and the whole world began to bring it — across the Pacific as well as across the Indian Ocean.¹⁶

A clarification that changes the reading. This reform was not invented at the top. It had been proposed as early as 1530, then tried out for decades in southern provinces before being extended to the empire.¹⁷

The state did not impose silver: it ended up ratifying a practice that was already established. Major decisions often look like this — less an invention than a generalisation.¹⁸

In other words, what kept the ships of this era moving was not only the European desire to see what lay elsewhere. It was also, and perhaps above all, Chinese demand.

⚠️ Simplifications to avoid: “Everything came from China” would be as false as “everything came from Europe”. What should be remembered is that a circuit has several ends, and that we often see only one of them.

Who did the digging

It remains to say who went down into this mine.

Before the Spanish, the Incas had an institution called the mita: each community had to supply men (mitayos) for a given period, for works of collective interest (roads, terraces, temples), in exchange for feasts and redistributions by the Inca state.

The Spanish viceroy reorganised this system and kept the word. But he changed its nature: the colonial mita became forced service in the mines. It is estimated that about one adult man in seven was requisitioned in the surrounding Andean provinces, each serving one year in seven.¹⁹

Conditions and survival in Potosí

Popular accounts sometimes speak of “millions of deaths” in the depths of the Cerro Rico. Historians specialising in mining demography (such as Peter Bakewell or Nicholas Robins) offer a more precise picture:

The service wore men out: maimed or sick, many young Andean men did not go home when their turn was over, whether they had served deep in the mines or in the refining mills.
From the 1570s onwards, the introduction of the process of separating silver with mercury (amalgamation) poisoned the refinery workers (trapiches).²⁰

A recurring device

What happened there is no mere detail: a new constraint was not merely imposed, it was given the name of an old institution so that it would look like continuity.

This is the third time this encyclopaedia has come across this device:

In Sri Lanka: Colonial engineers attributed to the ancient builders an invention they could not prove.
In Bali: An administration presented a control it had just established as traditional.
In the Andes: The hijacking of the mita.

📌 Key point: Those who dominate do not only write history; they also borrow the vocabulary of what they replace.

What travelled, and what is on our plates

Origin	Products / Items exchanged	Notes on cultural history
Americas ➔ World	Chilli pepper, maize, tomato, potato, bean, cacao, tobacco	Chilli reached China in the late 1500s as an ornamental plant (used for its heat 2 centuries later). The tomato remained a botanical curiosity in Europe for a century.
World ➔ Americas	Wheat, rice, sugar cane, horses, cows, diseases	Complete restructuring of American ecosystems and ways of life.
Maldives ➔ West Africa	Shells (cowries)	Shipped by the billion to serve as a currency of exchange in local and coastal markets.

Note 1

In 1972, Alfred W. Crosby wrote a book called The Columbian Exchange. In it, the historian tells the story of Columbus’s landing in 1492 through the ecological ramifications it had on the New World. […] I recently spoke with the retired professor about “Columbian Exchange”—a term that has worked its way into historians’ vernacular—and the impacts of some of the living organisms that transferred between continents, beginning in the 15th century.

“Alfred W. Crosby on the Columbian Exchange”, interview, Smithsonian Magazine, Smithsonian Institution