At the very end of Chapter 13, Diamond argues that the development and the maintenance of technology (to maintain technology, to Diamond, means to keep using it instead of "losing" it as some Australians in the north stopped using boomerangs, for example) depends on two things.
First, the presence of technology in a given area depends to some extent on local invention. If local societies develop agriculture and become sedentary, they can develop technology.
Second, technology in any given place needs to be helped along by diffusion from other regions. If neighboring societies have technology, a society can "borrow" that technology from them.
Therefore, to Diamond, the development and maintenance of technology in a given area depends on local invention (which itself depends on agriculture) and on diffusion from other societies.