Why did human development proceed at such different rates on different continents? Rather than providing a biological (racial) answer, Diamond claims that environmental factors account for the differences—as a professor of geography perhaps any other answer would sound unconvincing. Diamond attempts to sweep broad areas of history, the last 11,000 years or so, to provide some explanation.

A chief insight is the concept of underlying factors behind the proximate causes of events, like the European domination of the Americas. Guns, germs and steel constitute the proximate causes that are available because: 1) of the number of suitable plant specifies available for domestication which lead to 2) food surpluses, and in turn lead to 3) large, dense, stratified societies which could 4) develop the technology to create ocean-going ships and guns and steel weapons.