The answer to this can be found in Chapter 3. There, Diamond discusses how the Spanish, led by Pizarro, were able to defeat the Incas at Cajamarca. Diamond sets out a number of reasons why the Spanish were able to win. They include:
- Military advantages. Pizarro had steel swords. They had steel armor. They had guns and horses. The Inca had none of these.
- Diseases. Diamond argues that it is infectious disease that caused Atahuallpa to be at Cajamarca to be defeated by Pizarro. He says that Atahuallpa was there because he had been fighting a civil war. The civil war had been caused by the fact that the previous Inca emperor, as well as his designated successor, had been killed in a smallpox epidemic. This led to a succession crisis that caused a civil war.
- Political advantages. Diamond says that Pizarro came to be in South America because Spain had a more efficient and organized political system that could finance and organize the expedition to South America.
- Writing. Diamond says that writing allowed the Spanish to come to South America. Because Spaniards had written accounts of what they had seen in Mexico, more Spaniards came to the area to explore. It also allowed the Spanish to have more information about other cultures while the Incas had little information and could not handle the novelty of how different the Spanish were from them.
These are the factors that Diamond mentions in Chapter 3. He then goes on to explain in later chapters why the Spanish had these advantages.