The Spaniards' technology played a huge part in their defeat of the Incas in Chapter 3. It allowed them to get to South America in the first place (instead of having the Incas sail to Spain) and it gave them the ability to defeat more numerous opponents.
Diamond points out that it was Spanish maritime technology that allowed them to sail to South America. He points out that the Incas had nothing at all like ocean-going ships. Once the Spanish got to South America, technology helped them even more. Their steel swords, and their steel armor (and, to a lesser extent, their guns) were so much better than the weapons and armor the Incas had that the Spanish were able to defeat armies much larger than their own.
In these ways, technology allowed the Spaniards to reach South America and, once there, to conquer the Inca.