In interesting read:

1491; New Revelations of the Americas Before Columbus. Mann, Charles C. Vintage/Random House, New York. 2005/2011.

Behind all that it is always overpopulation.

are found, yet a maximum population of two million is assumed, then cities must have quite frequently been abandoned and new ones built.

I can't come up with whatever I read a while back that explained how the Mayan elites had to keep building ridiculously elaborate urban landscapes as a way of legitimizing their authority. But the paragraphs below give a pretty good idea of the result -- over-building led to deforestation led to drought led to collapse.

http://www.smithsonianmag.com/science-nature/why-did-the-mayan-civilization-collapse-a-new-study-points-to-deforestation-and-climate-change-30863026/?no-ist

In the first study, published Tuesday in the Proceedings of the National Academy of Sciences, researchers from Arizona State University analyzed archaeological data from across the Yucatan to reach a better understanding of the environmental conditions when the area was abandoned. Around this time, they found, severe reductions in rainfall were coupled with an rapid rate of deforestation, as the Mayans burned and chopped down more and more forest to clear land for agriculture. Interestingly, they also required massive amounts of wood to fuel the fires that cooked the lime plaster for their elaborate constructions—experts estimate it would have taken 20 trees to produce a single square meter of cityscape. . . .

Because cleared land absorbs less solar radiation, less water evaporates from its surface, making clouds and rainfall more scarce. As a result, the rapid deforestation exacerbated an already severe drought—in the simulation, deforestation reduced precipitation by five to 15 percent and was responsible for 60 percent of the total drying that occurred over the course of a century as the Mayan civilization collapsed. The lack of forest cover also contributed to erosion and soil depletion.

In a time of unprecedented population density, this combination of factors was likely catastrophic. Crops failed, especially because the droughts occurred disproportionately during the summer growing season. Coincidentally, trade shifted from overland routes, which crossed the heart of the lowland, to sea-based voyages, moving around the perimeter of the peninsula.

Since the traditional elite relied largely upon this trade—along with annual crop surpluses—to build wealth, they were sapped of much of their power. This forced peasants and craftsmen into making a critical choice, perhaps necessary to escape starvation: abandoning the lowlands. The results are the ornate ruins that stretch across the peninsula today.