The document discusses factors that can contribute to the collapse of civilizations, using the examples of Cahokia and Easter Island. For Cahokia, overreliance on corn as a single food source led to problems with nourishment and lack of enough farmland as population grew. On Easter Island, overharvesting of trees for resources led to their depletion and an inability to sustain population growth. More broadly, the document notes that lack of vital resources like land, food, water, and an inability to replenish or expand these resources can undermine civilizations.