The story of the conquest of Atahuallpa is crucial for Diamond's overall argument. In the series of events leading to his capture by the conquistador Francisco Pizarro, Diamond establishes what he calls the "proximate causes" of conquest. These include the use of military horses and of military technology such as steel swords, guns, and armor. Additionally the Incas were already suffering from the impacts of a smallpox epidemic. These factors, "guns, germs, and steel," are the immediate causes of conquest. Diamond's book is meant to uncover the deeper causes, and he argues geographic factors on the continents ultimately explain why conquest happened.
Diamond uses Thomas Edison to show that invention and social development are collective processes rather than acts of individual genius.
Diamond uses Gutenberg to show how the technology of literacy requires a social context in order to flourish.
Diamond uses an incident with Levi to ask why European immigrants came to own the land once possessed by indigenous people. Levi is Blackfoot, a Native American nation, and he worked for a Swiss immigrant farmer in the Midwest. On becoming angry with the farmer, Levi exclaimed, "Damn you Fred Hirschy, and damn the ship that brought you from Switzerland!"
Pizarro used "guns, germs, and steel" to easily defeat the Incas in 1532. Diamond takes this as the starting point for his book, asking why Europeans developed the factors that allowed them to easily conquer, through violence and disease, so much of the world. Diamond looks to geographic causes such as climates and crops that lend themselves to cultivation, sedentary populations, and resultant technologies and immunities.
Diamond cites Lévi-Strauss's ideas favorably as an influence on his work. Lévi-Strauss originated structuralism, a movement within anthropology that analyzes social relationships in terms of common structures. Diamond found his idea that the human mind is a structure shared by all peoples the world over particularly important.
Diamond cites Tolstoy's novel Anna Karenina to highlight a central idea regarding the development of civilizations. For things to go wrong, only one piece needs to fail. But for things to go right, every piece needs to develop and be used in exactly the right way. Success is thus very difficult.
Diamond shows how the invention of the steam engine was not the result of individual genius but the result of building on earlier developments and collaborating with various actors.
At the beginning of the book, Yali poses a question to Diamond. Using the local word cargo to mean material riches, Yali asks, "Why is it that you white people developed so much cargo and brought it to New Guinea, but we black people had little cargo of our own?" This main question is what Diamond is attempting to answer.
Jared Diamond is a science writer and the narrator of the book.