According to Jarod Diamond in Guns, Germs, and Steel, how did the Spanish easily defeat the Inca?

The answer to this question can be found in Chapter Three of Guns, Germs, and Steel, entitled "Collision at Cajamarca." Diamond argues that the same factors that caused the rapid and relatively easy defeat of the Inca led to similar outcomes throughout North and South America. Essentially, many of these factors are summed up in the title of the book: Pizarro and his men had guns, steel weapons, armor, and horses. The Inca had none of these things. The Spaniards also had Indian allies who backed their campaign against the Inca. But more important than these military factors was the fact that the Inca people had been devastated by smallpox, a disease brought by Europeans. Native Americans had not been exposed to these diseases, for reasons discussed by Diamond elsewhere in the book, and they thus had no immunity. As Diamond relates, the disease was especially destabilizing to the Inca, who saw their emperor and his heir fall victim to the disease. After their deaths, Atahualpa, the king that faced Pizarro at Catamarca, and a rival for the throne plunged the kingdom into civil war. "If it had not been for the epidemic," Diamond says, "the Spaniards would have faced a united empire" (77). So due to these factors, even though the Inca warriors outmanned the Spaniards 200 to one, Pizarro and his men, like Cortez and other conquistadores, managed a victory astonishing in its daring and its cruelty.