Diamond turns to a subject more familiar to most of his readership: the collision between the Incas and the Spanish in South America in 1532. In that encounter, Francisco Pizarro and 168 soldiers captured King Atahuallpa, who was supported by an army of 80,000 men.

Before his encounter with Atahuallpa, Pizarro stationed groups of men with guns and trumpets in strategic positions around a square. He even put rattles on his men’s horses so they would make more noise. When Atahuallpa and his entourage arrived, Pizarro presented the king with a Bible and a message about its contents. Atahuallpa, unable to read Spanish and offended by Pizarro’s manners, threw the Bible to the ground. The Spaniards attacked, killing Incan soldiers and capturing Atahuallpa while the Incan army, terrified by the Spaniards’ weapons and surprised into disorganization, failed to fight back.

After describing this scene, Diamond sets out to determine why the Spaniards were able to capture Atahuallpa. Pizarro’s soldiers’ weaponry was, by South American standards at the time, unimaginably effective. Horses had never been seen in South America before, and sixty-two of Pizarro’s soldiers were mounted on horses, giving them an enormous advantage of speed and force. Pizarro’s soldiers also had guns, steel swords, and steel armor, none of which existed among the Incas. These weapons were so much stronger than the weapons previously used in the Americas that Spanish armies of dozens or hundreds of men routinely slaughtered thousands of Indigenous people in battle.

In addition to superior weaponry, the Spanish conquest was aided by disease. The arrival of the Spanish in the Americas brought about a smallpox outbreak among populations that had never before been exposed to the disease. Whereas European communities had developed a resistance to smallpox over the course of centuries, the Indigenous people in South America had no such defenses. Whole communities died. Smallpox spread through the Incan empire more quickly than the Spanish could advance. Just a few years prior to Pizarro’s arrival in the area, an Incan emperor and his immediate heir had been killed. This brought about a civil war between Atahuallpa and his brother, who both claimed the Incan throne. Their conflict and the great loss of life it caused weakened the Incan civilization.

Smallpox was not the only disease that ravaged and destabilized Indigenous populations after Europeans arrived in the Americas. Measles, flu, typhoid fever, and plague all took their turns devastating populations around the world. Diseases sometimes harmed European explorers as well, creating problems for those who entered new territories and encountered new illnesses. In general, however, Europeans brought more diseases overseas than they found when they arrived.

Both the Incas—who had the most developed society in the New World at the time—and the Spanish had centralized, highly organized government systems. However, it was the Spanish and not the Incas who crossed seas and conquered other nations. The Spanish had developed maritime technology the Incas did not possess, and the Spanish had a written language, which allowed for better transfer of information over long distances.

Perhaps partly because of the lack of an Incan writing system, Atahuallpa had almost no prior knowledge of the Spanish before he encountered them. Therefore, he had no reason to suspect that the small Spanish force was a threat. If he had received information from the Native American groups that were conquered before the Incas, he might have suspected that the Spanish were likely to deceive him. He had no such information, however. He ordered his people to pay an enormous ransom to secure his release. Pizarro’s men collected this ransom and then killed Atahuallpa.

The next section discusses why the Spanish possessed advantages such as horses, steel weapons, maritime technology, writing, and the resistance to infectious diseases when the Incas did not.