Thank you, Catherine. Yes, civilizations do fall from many causes. Most often through a chain of circumstances, some totally outside the power of humans to deal with. Angkor Wat and Pompei were both cities and the civilizations of which they were a part did not fall with them. Pompei was destroyed by a volcano which even today we could not withstand. Ankhor Wat had unresolved issues with water management but as a Hindu religious center was gradually abandoned as its surrounding civilization became Buddhist. I am not sure how either applies to my argument.
The city of Mohenjo Daro was part of the great Indus Valley Civilization. The rivers from which it got its water supply depended upon the monsoon rains for replenishment. When the path of the monsoons shifted, those rivers were unable to support the local population density. This certainly was a natural phenomenon, but other cultures in the general area coped by creating effective irrigation systems. The Indus Valley Civilization did not.
The Inca Empire did not succumb to a natural disaster, unless one classifies the diseases, such as smallpox, inadvertently introduced by the Spanish, as natural — though they most certainly weakened the Inca. When Pizarro arrived, the Inca were in the midst of a civil war and many of the elite collaborated with the Spaniards to maintain their place near the top of the social hierarchy. Only after the conquest was complete did the Spaniards eliminate those collaborators.
The point I was trying to make is that civilizations all face threats and stresses. As long as they successfully deal with those threats and stresses, they survive. Civilizations decline and ultimately succumb when they either fail to recognize or fail to cope with those stresses. Historically, that failure has been one of a civilization’s greed and tribalism resulting in a lack of recognition, foresight, and cooperation — death by self-delusion and wishful thinking.