I know I'm a month late but I just discovered this community (subscribed btw!)

First of all this book is excellent, but it makes the opposite argument that OP claims. The entire point of the book is to illustrate that there is no "natural" way for humans to organize, and throughout history there is evidence that all manner of societies existed contemporaneously. Something Graber does repeatedly is highlight the many instances that totalitarian monarchies existed in the same geographic area at the same time as egalitarian democracies.

The impression he drills in over and over is that if people want a specific way to organize they must make it happen.