The answer to this can be found in Chapter 11, on p. 256 in the paperback edition of the book. There, Diamond lists four main ways in which ideas diffuse from one society to another. The vehicles of diffusion are:
- Trade. A society can receive new technologies simply by buying them from other countries.
- Espionage. Sometimes, societies spy on others and steal their secrets.
- Emigration. At times, ideas and items move from one country to another when people move between those two countries.
- War. At times, one country gains ideas from another by defeating the other country in a war.