How the Aztec and Inca Empires Fell

In November 1519, a Spanish soldier named Hernán Cortés stood on a stone causeway running north across Lake Texcoco and looked at a city most Europeans would not have believed possible. Tenochtitlan rose straight out of the water, a metropolis laced with canals and crowded with perhaps two hundred thousand people, larger than any city in Spain. Above its rooftops loomed the white pyramids of the Templo Mayor. The men beside Cortés had marched inland from the coast; some later wrote that they wondered whether they were dreaming. Within two years, that city would be a smoking ruin, its emperor dead, its empire dismantled. Eleven years after that, the pattern would repeat in the high valleys of the Andes.

How did this happen? It is tempting to imagine a handful of armored conquistadors simply overpowering empires of millions through superior steel and gunpowder, but that story is wrong in almost every detail. The conquest of the Americas was not a clean military victory. It was a collision of empires already under stress, a story of shifting alliances among Indigenous peoples, and above all a biological catastrophe whose scale still has no parallel in the documented human record. To understand the fall of the Aztec and Inca states, we have to look at the machinery underneath the legend.

A Generation of Practice in the Caribbean

The Spanish did not arrive in Mexico fresh from Europe. They arrived after a long apprenticeship. The Spanish presence in the New World began on the island of Hispaniola in 1493, and for roughly a generation it stayed confined to the Caribbean islands before any Spaniard set foot on the Mexican mainland. Those decades mattered enormously, because they were where the Spanish worked out the tools of colonization.

It was on Hispaniola that the Spanish invented the encomienda, a system in which the Crown granted a colonist the right to extract labor and tribute from a group of Indigenous people, in exchange for a nominal obligation to instruct them in Christianity. And it was in the Caribbean that the Spanish first witnessed what their arrival did to Indigenous populations: a demographic collapse so severe that the Taíno peoples of the Greater Antilles were reduced, within a few decades, to a fraction of their former numbers. By the time Cortés sailed for Mexico in 1519, the model of conquest and the engine of extraction were both already built. The mainland would simply be the place where they were applied at imperial scale.

The Empire That Cortés Walked Into

Central Mexico in 1519 was not a single unified state but the domain of an alliance. The dominant power was the Triple Alliance, a coalition of three city-states, Tenochtitlan, Texcoco, and Tlacopan, that together controlled much of central Mexico through a combination of warfare and tribute. The people we often call the Aztecs called themselves the Mexica, and Tenochtitlan was their capital, the island city Cortés saw from the causeway.

Two facts about this world would shape everything that followed. The first is that the Triple Alliance ruled by extraction. Subject peoples paid tribute, supplied labor, and in many cases provided captives for sacrifice, and a great many of them resented it deeply. The second is that not everyone had been conquered. The city-state of Tlaxcala, just east of the Valley of Mexico, had held out against the Mexica and remained an independent and bitter enemy. When Cortés marched inland, he was not entering a unified empire that would close ranks against an invader. He was entering a fractured political landscape full of communities looking for a way to break the Mexica grip. The Tlaxcalans, after fighting the Spanish first, chose to ally with them, and that alliance would supply the tens of thousands of warriors without whom the conquest is simply unimaginable.

A Captured Emperor and a City Holding Its Breath

On the eighth of November, 1519, the Mexica emperor Moctezuma II received Cortés at the southern causeway and lodged the Spaniards in the palace of his late father. Why Moctezuma admitted the strangers rather than crushing them at the lakeshore remains genuinely debated; the romantic notion that he mistook Cortés for a returning god is now treated with skepticism by most historians, and the truth was probably a mix of diplomatic caution, curiosity, and a desire to take the measure of these newcomers before acting.

Whatever his reasoning, the gamble failed. Within roughly a week, Cortés had taken the emperor effectively prisoner inside his own capital, holding him as a hostage and a puppet through whom Spanish demands could be issued. For months the city existed in suspended unease, its ruler a captive, its nobles uncertain, the small band of foreigners lodged at its heart and growing bolder. The arrangement could not last, and in the summer of 1520 it broke apart violently.

The Night the Spanish Fled

In May 1520, Cortés left Tenochtitlan and marched back toward the coast to confront a rival Spanish expedition sent to arrest him, leaving his lieutenant Pedro de Alvarado in command of the city. While Cortés was away, Alvarado ordered an attack on unarmed Mexica nobles and celebrants gathered for the religious festival of Toxcatl, slaughtering many of them in the temple precinct. The city, already strained, rose in open revolt.

When Cortés returned, he found his men besieged in their quarters with the population in arms against them. On the night of the thirtieth of June, 1520, the Spaniards attempted to escape Tenochtitlan in the dark along one of the causeways, and the retreat turned into a disaster. Weighed down by plunder, caught on the causeway with the bridges broken, they were attacked from canoes and on foot, and the great majority of the Spanish force and their allies were killed or drowned. The Spanish remembered it afterward as the Noche Triste, the Night of Sorrows. By any military measure, the conquest of Mexico had just failed. That it did not stay failed is owed to something the Spanish had carried with them without entirely understanding it.

The Invisible Conqueror

Early in 1520, a ship arriving from Cuba brought to the Mexican coast a passenger carrying variola major, the virus that causes smallpox. The Indigenous peoples of the Americas had never encountered it and had no acquired immunity. By the autumn of 1520, the disease had spread through the Valley of Mexico, and the toll was staggering. Smallpox may have killed something like a third of the population of Tenochtitlan in a matter of months, and among the dead was Cuitláhuac, the emperor who had succeeded the now-deceased Moctezuma and had led the resistance that drove the Spanish out.

The epidemic did not only thin the ranks of defenders; it shattered the leadership, the social order, and the will of a city in the middle of a war for its survival. This is the single fact that most reshapes the legend of the conquest. When Cortés returned to finish what he had begun, he did not face the city that had nearly destroyed him on the causeway. He faced a population in epidemic collapse, governed by a new and untested emperor, reeling from a catastrophe it could neither name nor cure. Disease did not act alone, but without it the siege that followed would almost certainly have gone the way of the Noche Triste.

Seventy-Five Days Around a Dying City

In the spring of 1521, Cortés came back to the Valley of Mexico with a transformed strategy. He had built thirteen brigantines, small sailing warships, hauled in pieces over the mountains and assembled to control the lake itself, cutting Tenochtitlan off from the canoe traffic that fed and defended it. Around him marched tens of thousands of Indigenous allies, Tlaxcalans above all, who provided the overwhelming bulk of the fighting force and made the siege possible at all.

The siege of Tenochtitlan lasted seventy-five days. The Spanish and their allies fought their way along the causeways, filling canals, demolishing buildings as they advanced so that the Mexica could not counterattack from the rooftops, and slowly strangling a city already gutted by disease and now cut off from food and fresh water. On the thirteenth of August, 1521, the last Mexica emperor, Cuauhtémoc, surrendered. Tenochtitlan was burned, and with its fall the conquest of central Mexico was effectively complete. The Spanish would build their colonial capital, Mexico City, directly on the rubble.

Pizarro Replays the Pattern in the Andes

What happened in Mexico was not a one-time accident, and the proof is that almost the same sequence unfolded again a decade later, two thousand miles to the south. The Inca empire, Tawantinsuyu, was the largest state in the pre-contact Americas, stretching along the Andes from modern Colombia to Chile, bound together by roads and a sophisticated administration. And like the Mexica, it was struck by disease before it was struck by Spaniards. Smallpox, spreading overland ahead of the conquistadors themselves, reached the Andes and killed the Inca ruler Huayna Capac along with his designated heir, throwing the succession into chaos and igniting a civil war between two rival sons, Atahualpa and Huáscar.

Francisco Pizarro arrived to find this empire torn by internal war and weakened by epidemic. On the sixteenth of November, 1532, at the highland town of Cajamarca, he met the victorious Atahualpa, ambushed his entourage, slaughtered his unarmed attendants, and seized the emperor himself, exactly the combined mechanism Cortés had used in Mexico: a captured ruler, Indigenous factions willing to ally against a hated overlord, and a population already devastated by disease. The Inca paid an enormous ransom in gold and silver for Atahualpa's release, and the Spanish executed him anyway. The conquest of the Andes would take longer and face fiercer resistance than the conquest of Mexico, but its decisive opening move was a near-perfect replay.

The Machinery of Extraction and Its First Critic

The fall of the two great empires was the beginning of the colonial system, not the end of the dying. Once the conquest phase ended, the economy hardened into the encomienda, the institution the Spanish had first built in the Caribbean. Indigenous communities were assigned wholesale to individual Spaniards, who extracted their labor and tribute in return for the nominal obligation of Christian instruction. In practice the encomienda was a machine for working people to death, and the mortality it produced rivaled that of the epidemics themselves.

The numbers are almost impossible to absorb. Pre-contact central Mexico is estimated to have held somewhere between twenty and twenty-five million people. By the year 1600, that population had fallen to between one and two million. This collapse, the deepest demographic catastrophe in the documented human record, ran on smallpox, measles, and typhus working together with the brutal labor conditions of Spanish rule. Against this backdrop, a Dominican friar named Bartolomé de las Casas became the system's fiercest internal critic. In 1542 he presented his Brevísima Relación de la Destrucción de las Indias, a furious indictment of Spanish cruelty, to the court of Charles V. The New Laws that followed attempted to limit the encomienda, with mixed and often-evaded results. Las Casas had aimed to reform an empire from within, but his text was later translated abroad and turned into anti-Spanish propaganda, feeding what became known as the Black Legend, the enduring image of Spain as uniquely cruel among colonizers.

Key Takeaways

Between 1519 and 1521 Hernán Cortés destroyed the Mexica state not through European arms alone but through a combination of three forces: the tens of thousands of Indigenous allies, above all the Tlaxcalans, who supplied most of the fighting power and seized the chance to break the Triple Alliance's tribute empire; the strategy of capturing the ruler, which he applied to Moctezuma II and which collapsed during the disastrous Noche Triste of June 1520; and a smallpox epidemic that reached Mexico in early 1520, killed perhaps a third of Tenochtitlan including the emperor Cuitláhuac, and left a gutted city to face the seventy-five-day siege that ended with Cuauhtémoc's surrender on the thirteenth of August, 1521. Francisco Pizarro replayed the identical mechanism at Cajamarca in November 1532, exploiting an Inca civil war that smallpox had already triggered. What followed the conquest was the encomienda, the extraction system first built in the Caribbean, which alongside disease helped reduce central Mexico's population from roughly twenty to twenty-five million before contact to between one and two million by 1600, and which drew its first sustained European critique from Bartolomé de las Casas in 1542.