[jcranmer]

North American agriculture appears to have been cursed with poor cereals for cultivation--basically none of those crops survive today as major cereal crops, unlike all the other agricultural hotspots. Corn doesn't arrive until ~1000, and the arrival of corn radically alters the makeup of North America.

Cahokia is the largest city of North America (peaking at probably 10-20k people), starting about 1050, peaking perhaps 1200, and being completely abandoned by about 1350 for unknown reasons. And after Cahokia, there's... no other major city. Mississippian sites in general decline in size, and there seems to be a general aversion to urban centers. It's hard to make out what is going on, because then comes catastrophic European contact that destroys all of the cultures with only fragmentary evidence of contemporary lifestyle.

One theory that I've heard is that we're seeing what is essentially the endgame of proto-civilization: the North American cultures are trying out alternatives to urban, territorial polities. Perhaps something akin to Greece during the Greek Dark Ages. If European contact had come two or three centuries later, we might have seen the emergence of territorial states in North America.

The exception to this in North America is of course the Southwest, which was in cultural contact with South America and Mesoamerica. Corn arrives to the Southwest far earlier than the rest of North America--maybe 2000 BC at the earliest, although it doesn't clearly hold until about 500 BC.

[anthonypasq]

this seems so bizarre considering how incredible fertile the midwest is considered. you'd imagine the mississippi river system had enough geographical advantages to support the number of people you would see in China or India