As I understand it, Jared Diamond and his "geography is what made some races great" idea are very discredited. Outright hated even. I'm not going to change anything, but he really had an agenda, so his ideas are really not too right.
Free advice usually isn't.
A minor point, perhaps, but while it is true that the "civilized" urban classes generally had guaranteed access to food, they often did not have access to better food. Quite the opposite in many cases. Just think of the Roman plebs, many of whom were fed primarily on government-provided (government being, perhaps, a somewhat inaccurate term) bread, whereas the average "barbarian" tended to have much better access to meat and a more varied diet. It is probably no accident that Roman soldiers were known for being significantly shorter than their Celtic and Germanic opponents, which of course made the Celts and Germans seem even more frightening and alien (arguably the original meaning of the word barbarian) to the average Roman.
I'm sure Son of Zorn should be on here, but I've never watched it. Could someone with more knowledge add it?