Unlike other vanished civilizations, at least some of the Mayans' written records have survived, which has enabled scholars to partially reconstruct their history. But those tantalizing clues have only made the mystery of their decline more frustrating [source: Diamond]. Over the years, researchers have developed various theories about what caused the decline of Mayan civilization. Here are three of the most prominent ones:
- Over-farming. Some scholars have argued that Mayan society grew too rapidly for its own good. As the population increased, it put farmers under more and more pressure to grow food, and gradually, they ran out of fresh forest land to clear. That would have forced them to plant crops in their fields without an adequate fallow cycle -- that is, the time that it takes soil to rebuild its nutrient supply [source: McKillop].
- Warfare. The Mayan rulers, who convinced their population that they were powerful enough to control the weather, may have started to believe their own hype. Their efforts to conquer neighboring peoples may have backfired, as long periods of war sapped Mayan resources and led to retaliation. There's evidence that a number of Mayan cities eventually were besieged and fell to invaders [source: McKillop].
- Disease. In a 1979 article, researcher James L. Brewbaker theorized that Mayan society collapsed due to disease -- not a human epidemic, but an agricultural one, maize mosaic virus, which destroyed their food supply [source: Brewbaker].
While scientists aren't completely discounting all those possibilities, in recent years they've added another theory. Increasingly, they suspect that Mayan society collapsed because of the stress of climate change -- a risk that faces modern civilization today, as we burn huge amounts of fossil fuels and spew greenhouse gas emissions that warm the planet. The Mayans, though, didn't have gas-guzzling SUVs, and they didn't need coal-burning power plants to power their big-screen TVs and air conditioners, since they didn't have those either. So what was the deal with them? We'll look at possible explanations in the next section.