[IYAS9YAS]

But rather than developing, like London, into a modern metropolis, Cahokia is more like the fabled lost continent of Atlantis. Having become a major population centre around AD1050, by 1350 it was largely abandoned by its people – and no one is sure why. Neither war, disease, nor European conquest drove Cahokia’s residents from their homes. Indeed, the first white man to reach these lands, Spanish explorer Hernando de Soto, didn’t do so until 1540.

Many of the thriving areas in the southwest were abandoned around that time period, as well. Something drove them to other places. My bet is weather patterns changed drastically for a period long enough to convince them to leave.

[sima_yi]

Little Ice Age?

[RayChuang88]

My bet is weather patterns changed drastically for a period long enough to convince them to leave.

Remember the Dust Bowl that drove farmers out of the Midwestern USA from 1932 until 1938, when the rains finally returned to normal? An similar weather event some time between 1300 and 1350 AD probably did the same thing.

[MNJohnnie]

Global Cooling?

The Medieval Warm Period (MWP) also known as the Medieval Climate Optimum, or Medieval Climatic Anomaly was a time of warm climate in the North Atlantic region that may have been related to other warming events in other regions during that time, including China[1] and other areas,[2][3] lasting from c.;950 to c.1250

https://en.wikipedia.org/wiki/Medieval_Warm_Period