Why did the Maya disappear?

The question has fascinated scholars and the public since 19th century explorers began dsicovering ¨lost cities ¨in the Petén: How could one of the ancient worlds great civilizations simply dissolve?
Early speculation centered on sudden catastrophe, perhaps volcanism or an earthquake or a deadly hurricane. Or perhaps it was a mysterious disease untraceable today _something like the Black Death in medieval Europe or the smallpox that wiped out Native American Populations at the dawn of the colonial age. Moderns researchers have discarded these one-event theories, however, because the collapse extended over at least 200 years. ¨There isn´t any single factor that everybody agrees on¨says Southern Illinois University´s Prudence M. Rice
From National Geographic, Aug. 2007, p98