The main idea of Chapter 4 of Guns, Germs, and Steel is that it is farming societies that are more able to have the “guns, germs, and steel” that allow them to become rich and powerful. The chapter is entitled “Farmer Power,” clearly showing us its main theme.
To understand the main theme of Chapter 4, simply look at Figure 4.1 on p. 87 in the book. This figure shows us Diamond’s argument in this chapter. He is arguing that farming societies have the ability to create technology, to have political organization, to have horses and writing, and to have epidemic diseases. All of these things make them stronger than non-farming societies.
Diamond says that farming societies can become sedentary. He also says that they can support higher population densities. Both of these things allow them to develop technology. They can develop technology because they stay in one place instead of having to carry everything they own with them as they migrate. They can develop technology because they have more people in one place, thus giving them more potential inventors and more people who can specialize in things like creating technology or learning to write.
Diamond also says that farming societies have other advantages. Horses give them greater mobility and more military power. Epidemic diseases give them a “weapon” that they do not even know about. These diseases can decimate hunter-gatherer populations that do not have any immunity to them. In these ways, farming societies become more powerful than non-farming societies. This is the main point of Chapter 4.
One piece of evidence can be found on p. 91. There, Diamond demonstrates that horses helped various societies become militarily dominant over societies without horses. He cites, for example, the Hyksos who were able to conquer Egypt because they had horses and the Egyptians did not.
A second piece of evidence comes from the British conquest of New Zealand, discussed on p. 90. Britain was a farming society that could produce enough food to support a large professional army. The Maori were well-armed and warlike, but they could not support a large army because they did not have farming. This allowed the British to defeat them.