Geography.

That in essence is Dr Diamond's ultimate answer for why we see such disparity in human populations today and throughout history. Europeans were able to conquer the New World and not the other way around because of geographical factors giving them numerous advantages beginning with food production and leading to technology and immunity to disease. It was not because of some innate superiority of the European people, which is often the sort of argument put forward, and in the most extreme cases, used to justify exploitation or genocide.

This is an excellent book, thoroughly researched, logically and soberly argued, and including fascinating insights gathered by the author himself in New Guinea, a microcosm of human societies. What does the future hold for human societies? While geography perhaps plays a smaller role in modern times, lessons about human societal structures produced by geography may prove invaluable for the future success of humanity.