I have just discovered in my vegetable garden an ancient stone tablet that describes in detail why the Mayan civilization collapsed. Its author was an astrologer named Krugmanetlan the Shrill. Here is what he carves:
The Priests began selling assurances of rain to the farmers. If the farmers wanted rain, they had to pay the priests. As the population grew, the farmers needed to farm more land to feed the people. However, if the farmers wanted to farm more land, etc., they needed more rain. This created a natural upper limit to the amount of money the priests could generate from their assurances, which is represented by the equation I=MfkD, where I is income, Mfk is the total milk, fiber and korn that can be produced by the land, and D is beer.
Therefore, the priests began lending money to the farmers so they could farm more land and buy more assurances of rain. Some farmers discovered that by placing themselves into massive debt to the priests, they could produce enough milk, fiber and korn to become incredibly wealthy themselves, which allowed them to pay extra money to the priests to short the other farmers their portions of rain, destroying their farms and driving them out of business. Thus land became cheap. Then the farmers discovered that they could sell their own version of assurances back to the priests, with the guarantee that if in fact it didn't rain, contrary to what the priests had assured, they would pay the priests a guaranteed portion of their crop with which to offset the losses on the priest's assurances. That way the priests made money no matter what happened, thus allowing them to take on more risk and promise more rain so more land could be cleared for farming, and more loans could be taken out for more assurances of rain. Much wealth was generated in this fashion, where it had never existed before.
For many centuries, this formula worked because rain was thought to be a constant. Then one year it didn't rain. The farmers couldn't pay the priests against their losses on assurances, because they had no crop, because it hadn't rained! (see Figure of Krugmanetlan Slapping his Jaguar Forehead) The farmers sued the priests for payment on their assurances, but the priests couldn't pay because they were suing the farmers for payment on their assurances. And all their combined wealth, which had never existed, suddenly evaporated and their civilization collapsed.
Eventually, the people ate the priests and farmers until there was no one left who knew how to pray for rain or plant a crop. So they all walked off into the jungle to hunt monkeys, etlan.