To Diamond, the "ultimate factor" that determines which societies become "haves" and which become "have nots" is geography. Societies that developed in places that had many domesticable plants and animals had an advantage, particularly if it was easy for those species to spread across a large area. So geography is the major cause of the fact that some societies became richer and more powerful than others.
More proximate causes are technology, epidemic diseases, and political organization. The political organization allowed some societies to extract taxes from their people and then to create centralized governments with militaries and bureaucracies. Such societies had an advantage over less organized ones. The impact of technology and diseases are more obvious. Technology allowed some societies to be more powerful economically and militarily. Diseases allowed some societies to decimate the populations of others without even trying.