When the Inca ruler Atahualpa first met the Spaniards outside Cajamarca in 1532, one of Francisco Pizarro's lieutenants rode straight at him and his court. The horse stopped inches from Atahualpa's face, snorting. Atahualpa did not move, said he was unimpressed and told the visitors he would meet their commander when he chose. After they left, military historian Si Sheppard said, Atahualpa had every member of his court who had flinched or shown fear executed, including generals, to make the point that these strangers were not to be feared.
Atahualpa later became Pizarro's prisoner. Sheppard, a military historian and author of a book on the 1536–37 siege of Cuzco, told that story on the Dwarkesh Podcast, in an episode published October 1, 2026. Two questions ran through it. What exactly gave a few hundred Spaniards such an advantage in battle? And why could Aztec and Inca societies, whose adult men all trained for war, not neutralize that advantage once they understood it?
The episode description points out how lopsided the numbers were. Hernán Cortés and a few hundred conquistadors brought down an Aztec empire of about 6 million people within two and a half years. Pizarro did the same to an Inca empire of about 10 million a decade later. The description also says Indigenous fighters made up 99% of the conquerors' forces. Those alliances are a separate story. This one is about what the Spaniards did on the battlefield.
Guns, germs and steel, reordered
Sheppard said Jared Diamond's book Guns, Germs, and Steel first drew him to the subject. Diamond's title lists the advantages the Spaniards had brought from Eurasia. PBS's background to the 2005 documentary explains Diamond's argument: the advantage came from capabilities that had built up and spread across Eurasia over a long time, not from any difference in the abilities of individual peoples.
Sheppard ranked those advantages differently from the title. "Guns in reality weren't so significant," he said. Firearms of the period took so long to reload that, once the first shock wore off, native fighters realized they were not great assets in battle.
Steel was a different matter. Local weapons were made of wood, stone and obsidian, a volcanic glass. Sheppard said obsidian could be razor sharp and dangerous for slashing, but it did much less against steel armor and, above all, steel helmets. The Spaniards also brought Old World fighting traditions and long blades made of Toledo steel. They used these to thrust. A warrior who raised his arm to cut or slash left his side open, and a thrusting blade could hit him there first. Sheppard said the edge came from the technology combined with "generations of inherited military training and skill."
The Spaniards were not invincible. Sheppard said Cortés took casualties in hand-to-hand fighting. He buried his dead under the houses where his troops sheltered, so the enemy would not know it was having any success. "It was as much a mind game as it was a physical game," Sheppard said.
The horse
In Sheppard's account, the decisive weapon was the horse. "I cannot emphasize or overemphasize enough how vital the horse was," he said. Sailing ships let the Spaniards land anywhere along the coast. Once they went inland, "the horse was decisive."
The Americas had nothing like it. Horses had evolved in North America but had died out there. Sheppard said local peoples lacked not only horses but beasts of burden in general. The Inca had llamas, which carried their army's baggage in pack trains that stretched for miles. The Aztecs' only domestic animals were the turkey and the chihuahua. The Spaniards also brought armored war mastiffs trained to take down men.
Sheppard said horses worked in both directions. In an attack, cavalry could break through any native formation that lacked the weapons, training or discipline to stand against a mass charge. When things went badly, the riders could retreat faster than the enemy could chase them.
Cajamarca
Sheppard said Pizarro reached Cajamarca with 168 men. Atahualpa had just won an Inca civil war and was on his way to be enthroned in Cuzco. Sheppard said Atahualpa's envoy advised him to kill the strangers by setting fire to their quarters at night, since they slept together. Atahualpa saw an opportunity instead. He sent tens of thousands of men to block any retreat and came to meet Pizarro with his army. Sheppard repeated a Peruvian saying: Atahualpa planned to have Pizarro for lunch, but Pizarro had him for breakfast.
The Spaniards were frightened. Sheppard said the Inca army's campfires on the hills the night before looked like twinkling stars. When the Spaniards watched Inca troops filing into the courtyard, some admitted they were losing control of their bladders. Once Atahualpa was inside that narrow courtyard, Pizarro sprang the ambush. His cannon and arquebuses, early muskets, opened fire, his horsemen charged, and Atahualpa was taken prisoner.
Sheppard said the guns did very little physical damage, but the Inca had never heard gunpowder before. The founder of their empire was Pachacuti, a name Sheppard translated as "the thunder bearer." Seeing strangers who seemed to control thunder, he said, "must have been just beyond shocking." Then the horses charged, ridden with stirrups by men who had trained in the saddle. Sheppard called Atahualpa's men veterans and the winners of a civil war, but said they had never seen a horse. "They had no doctrine to push back against that," he said. Men crowded against the courtyard walls trying to climb out until the walls collapsed under their weight. Spanish riders chased those who escaped across the countryside and stopped only when night fell. Faced with something entirely outside their experience, Sheppard said, "the flight was the winner in this instance."
Figures raised in the discussion put the Inca dead at close to 10,000 against no Spanish deaths; they are not verified here. Sheppard said the only Spanish injury was to Pizarro himself: a comrade swinging his blade cut Pizarro's hand as Pizarro reached to seize Atahualpa. Hernando Pizarro's letter of November 1533 also describes Francisco's hand being cut by another Spaniard during the capture. Hernando, a member of the expedition, describes the Spaniards hiding in buildings around the plaza with horsemen ready and an artillery shot as the signal to attack. He separates Atahualpa's larger army outside the town from the roughly 5,000 to 6,000 attendants who entered the plaza. His letter was addressed to imperial authorities and includes religious and legal justifications for what the Spaniards did.
Why not just swarm the riders?
The obvious objection came up in the discussion: with tens of thousands of men, couldn't the defenders accept losses, mob a rider and drag him from the saddle? Sheppard said Europeans knew how to beat cavalry. The Swiss had shown that a mounted knight could be unhorsed and defeated by men standing shoulder to shoulder with long pikes, which kept the horses back and broke the force of their charge. But that took the right weapons and also "the discipline, training and institutional knowledge" to use them. Mesoamerican warriors fought in loose formations with plenty of space between them. Sheppard said that was the worst arrangement against cavalry, because horses could ride straight through the gaps.
He rejected the image of pre-Columbian societies as "childlike" or unable to respond. Both the Aztecs and the Inca, he said, tried countermeasures at every level.
The countermeasures
One was fighting in tight spaces. When Cortés returned to Tenochtitlan in 1521, the Aztecs drew the Spaniards into a city of islands linked by bridges and causeways, which Sheppard said minimized the horses' advantage because it was not good horse country. Defenders threw stones from the rooftops and cut man-sized holes between buildings so they could slip from one to the next where horses could not follow.
Another was water. Sheppard said the Aztecs broke the dikes of Lake Texcoco to flood a smaller lakeside city that Cortés was attacking. In water, metal armor dragged men to the bottom. The town is likely Iztapalapa, where the conquistador Bernal Díaz describes defenders cutting two dams. Díaz's account differs in its details. He says Indigenous allies drowned, Spanish gunpowder was ruined, and the expedition withdrew under further attack. Sheppard said the Inca later flooded a river against the Spaniards at Ollantaytambo. Mark Cartwright's history of the siege says Manco Inca diverted the Vilcanota River there in January 1537. The flood covered ground that suited cavalry, and Hernando Pizarro's force withdrew to Cusco.
The defenders also adapted Spanish weapons. Sheppard said they tied captured swords to the ends of long poles to make improvised pikes, working out without being taught that long spears could hold horses off. Díaz likewise records Mexica fighters preparing long pikes fitted with captured Spanish swords. The Inca used bolas, weighted cords they had hunted large birds with, to tangle horses' legs. Sheppard described one Aztec warrior who let a conquistador's lance pierce him, then held onto it so his comrades could pull the rider from the saddle. The Aztecs made Spanish prisoners show them how to use captured crossbows. The Inca made captured Spaniards teach them firearms. Manco Inca, who led the Inca resistance, learned to ride to show his people it could be done. María Concepción Bravo Guerreira's 2003 study of conquest chronicles and colonial records describes similar Andean tactics against cavalry, including traps for horses, deliberate flooding and choosing ground that riders could not reach.
"So they were trying," Sheppard said, "but the learning curve was so steep and the timeframe to internalize foreign technology and foreign tactics was too short."
Mistakes or constraints?
The discussion then turned to what looked like plain blunders. Aztec warriors had Cortés on the ground several times but tried to drag him off alive for sacrifice instead of killing him. Commanders wore elaborate regalia that made them easy for cavalry to find, and killing a commander could make a whole army flee. During the Inca siege of Cusco, the attackers let a few hundred Spaniards rest at night instead of rotating fresh troops to wear them down. How could warrior societies, compared to Sparta, fail to improvise as Cortés and Pizarro did?
Sheppard's answer was that these habits were part of the culture. Aztec warriors gained status by bringing captives back to Tenochtitlan for sacrifice. He said there was even a ranking of prisoners, with several captives of one group worth a single Chichimec, because the Chichimecs, a wilder northern people, fought more fiercely. He noted that medieval Europeans also preferred to take enemies alive so they could ransom them, and that two French kings were captured that way, after the battles of Poitiers and Pavia. In one sense, he said, the Aztec model made more sense, since a sacrificed enemy never came back to fight again. Because the practice was bound up with religion, he said, it could not be changed within a few years. He compared it to asking people fighting aliens to give up Christianity because another faith would make them better soldiers.
On Cusco, Sheppard pointed to the Spartans holding the pass at Thermopylae, as in the film 300. The surviving Spaniards fell back into two heavily fortified buildings with narrow entrances, and Cusco's streets were narrow too. However many men the Inca had, only a few could come down those streets at once. A small number of men in metal armor, joined by a growing number of native allies, could block them. When pressure eased, the Spaniards sent their horses into the wider plazas and the countryside to attack isolated groups. As the siege dragged on, Sheppard said, men slipped away at night. Some changed sides, and many were from subjugated peoples with no loyalty to the Inca. Most needed to get home to bring in the harvest before winter, or face hunger the following year. Cartwright's account also names the harvest as a limit on how long the besieging army could keep up its pressure.
Sheppard said there was one situation where Spanish advantages would have counted for nothing: the whole Spanish force caught in a mountain pass. Horses cannot charge up steep slopes. With boulders and trees blocking both ends, the infantry could not move either, and metal armor would not protect anyone from a two-ton boulder. Hernando Pizarro's letter admits that steep mountain passes could have stopped the mounted troops if anyone had defended them. Sheppard said such traps worked on a small scale. Cartwright describes the Inca commander Quizo Yupanqui destroying Spanish relief columns in ravines. But catching the entire Spanish force in one place at one time, Sheppard said, never happened. In his closing words on the question: "Again, it's that shockingly short, steep learning curve. It just wasn't enough time."
How small the edge was
Near the end, the discussion returned to how modest the Spanish technical advantage looked: guns that did little in battle, leaving swords and horses. It also noted that the Spaniards even gave up some of their own armor partway through the conquests. Sheppard explained that they always kept their helmets, but many swapped metal body armor for the local cotton armor. Cotton was good enough against local weapons, gave them more freedom to move and was less tiring to wear. They would not have taken that approach back to Europe, he said, because there it would have left them too vulnerable. The episode description presents the conquests as a precedent for an alien force taking over a larger, established order, which is how people sometimes picture an AI takeover. On the battlefield, in Sheppard's account, the invaders' edge came down to steel blades and horses, which their opponents had never had the time to learn to beat.