I read your blog fairly often so was quite surprised to see you talking about my book. I'm sorry you thought I was being "slippery" in not specifying more often when I was talking about the area north or south of the Rio Grande. You probably saw an artefact of my struggle with terminology. Problem is, the way we divide things up now (splitting the area north of Colombia into North America and Central America) doesn't fit very well with how things were then, when you had a bunch of related, highly urbanized societies in a region extending from about the Honduras-Nicaragua border to the American SW, and then everything else. In earlier drafts I tried saying when referring to the not-as-urbanized places something like "the area north of the Rio Grande except for the Southwest," but this was shouted down by my editors. I tried not using that kind of label as much, and hoping the reader would catch on to what area I was talking about, but obviously that didn't work for you. My apologies .
No, I should apologize. I was rushing to feed the blog beast after a spell of computer troubles and I posted something quick and dirty about an impressive book that Mr. Mann had clearly worked on for years, a topic where experts hold conflicting views, which he rightly refused to oversimplify.
I would say, though, that you're not quite right about Cahokia. Cahokia was by far the biggest of the mound cities of the SE and Mississippi Valley, but there were many thousands of these places--ten thousand is the estimate I've heard most often. Most of them probably held 3-10,000 people, so they weren't huge places. It's as if the moundbuilders went straight past urbanization to suburbanization, skipping the cities and going right to the strip malls. A lot of these places are just a few miles apart, and presumably would have had maize fields between, exactly the sort of situation that most urban historians think would have led to cities.
The other thing is... ten thousand of these places. If you do the math, 3K x 10K = 30M = far more than the total number of people supposed to be north of the Rio G (<20m).>
Another interesting topic would be the population of California Indians -- how dense can a population in a pleasant climate but fairly dry get without agriculture? We know the Northwest Indians were pretty thick on the ground due to fish, even without farming, but California Indians didn't leave a lot of relics behind.
I would argue with you a little that urban life was MORE feasible in the New World than the old because of the lack of pathogens. A lot of archaeologists think that it was LESS feasible because of the lack of draft animals, which made communications and infrastructure-creation much harder. It seems to me that the situations were so different that it's hard to make useful comparisons. Mesoamerica was almost freakishly urbanized, with some geographers claiming it was the most urbanized place on Earth in 1000-1400. But the second most urbanized place was China, which was absolutely swimming in disease. You can look to Africa for insight, as you do, but the situation is muddy. In Sub-Saharan Africa you certainly had major cities--Great Zimbabwe, Ingombe, Mbanzakongo, Loango. But there weren't as many packed in as Mesoamerica, that's for sure. A good book on this is Chris Ehret's Civlizations of Africa.
The Yucatan Peninsula is a horrible place -- not just hot and humid, but the limestone soil means that water sinks into the ground almost immediately. It's completely flat, with no rivers or lakes, and covered with low scrubby trees about 15 feet tall. Looking out the back window of a hotel room on a beautiful beach in Cozumel, I had a hard time shaking the feeling that I was an astronaut in some Twilight Zone episode who had landed on a planet where the beach was wonderful, but the rest of the planet was just a cheap backdrop slapped together in some alien movie studio. And yet the Mayans built extraordinary urban centers like Chichen Itza and Tikal on this unpromising landscape, while North American Indians, blessed with a temperate climate and rich soils, rarely created cities.