I think that the reason the Mayans at Copan collapsed was because of they overused the soil. When the Mayans were farming they didn't know that each crop they planted required certain vitamins, and after years and years of planting the same crop in the same spot all the vitamins they needed to grow their food were sucked out. So as the soil lost it's vitamins the corn began to die, and the people began to starve. The farmers today say that they have to plant corn every year, and the land has no time to rest, with around the same number of people to feed. I think that it would make sense that the corn would die and the Mayans would lose most of their food supply. The evidence from a lot of the skulls people have found say that most of the people died from malnourishment, which would make sense if their crops died. Corn can also cause an iron deficiency, or amenia, which was found in many of the skulls of the Mayans, so they could have really relied on it.
The unfinished monuments that the Mayans left could have been from all the carvers dying, and losing their energy so they can't work as long as they would have been able to. Over-farming could have produced the erosions that destroyed their houses, and hundreds of years later after the soil had rejuvenated forests could have developed.
