<i>Guns, Germs, and Steel</i> is a really good book. Two hospital MD's independently stopped me at gym to say "that's one of the best books I've ever read." And the department chair where I worked exclaimed similarly.<p>Another hypothesis I would posit about the evolution of world powers is that WWII Axis members later reached population maximums and declines <i>before</i> Allied powers, and that that somehow shaped their political and situational values to align them together. It's not obvious until you see population graphs of Japan, Italy and other Axis countries are nearly all in population decline unless other unqiue factors like immigration bolster their numbers.