[dan_mctree]

To my untrained eye, the eastern United States and Uruguay + surroundings also seem like great places for civilizations to thrive. But for some reason those areas did not seem to have particularly large civilizations before the colonization period. Does anyone know of a good reason why these areas were relatively unpopulated compared to the areas you mention but also compared to say Mexico?

[brabel]

Do yourself a favour and just read the book we're talking about. It explains exactly these questions, and many more, even if the current trend is to criticize those explanations because "there could be other factors as well" (which Diamond does acknowledge, but perhaps not enough for everyone).