[piasa]

1250-1350 AD was the last of the late Mississippian occupation at Cahokia mounds on the Mississippi River flood plain. At the time Cahokia was the largest city in North America north of present day Mexico, and was larger in population than London.

After centuries of living there they abandoned the city.

[yefragetuwrabrumuy]

There is a theory that the regular rise and fall of such kingdoms was because they lacked any theory of conservation.

The exception to the rule was Egypt, because unlike most everywhere else, they had only one great agricultural season a year, starting with the flooding of the Nile river. This both restored and fertilized the farmland, and they knew with some accuracy how much to plant. And the rest of the year they did other things.

But the rest of the world would over time deplete the area around a kingdom of lumber, crops would deplete the soil of nutrients, irrigation would salt the soil reducing yields, etc. The end result was that over time, everything had to be transported from further and further away.

In Mexico and central America, the ruins of former cities were so evident later kingdoms became very fatalistic and apocalyptic, just assuming that sooner or later they would fail as well.