I am presently reading "Collapse" by Jarod Diamond, and he states that there are 5 factors why past societies collapsed:

1 Environmental Damage
2 Climate Change
3 Hostile Neighbors
4 Loss of Trade, or difficult trade relations with other societies
5 A society’s response to environmental factors

The past collapsed civilizations which Diamond wrote about were Easter Island, Pitcairn Island, Henderson Island, the Anasazi, the classic Lowland Maya, and the Greenland Norse.

Easter Island is interesting because here was a civilization that used intelligent engineering techniques (that we are not sure of) to move 50 to 80 ton pieces of stone and then hosted them by I guess some kind of pulley system into an upright position. But in the process of creating all the statues on the island, the people cut down all the trees, creating irreparable environmental damage to the island. The people used all the trees to move the statues from the quarries to where they wanted then to be, and used trees to create the pulleys systems and rope to stand the statues upright. My question is if these people were smart enough to move 80 ton rocks, why could they not understand that by cutting down all the trees they were harming their way of life? Why did they have to make so many statues in the first place? Why was not 1 sufficient? If they only made 1 or 2 statues the people might still be there and the trees would have protected the island from erosion, they would not have had to use stones to try to protect the fields from wind and erosion.

The other interesting thing was how cannibalism played a part at the end of the Easter Island civilization. Here is an intelligent civilization reverting to cannibalism because of deforestation and other human environmental impacts to the island. If something happen here in America ( a natural disaster of some kind) creating a massive societal and food disruption would we as a society revert to cannibalism to survive and justify it?