I had a mind-boggling experience today. I visited an Anasazi site in Aztec New Mexico (google Aztec Ruins New Mexico). It was mistakenly thought that the pueblo was Aztec, but it ain't. It was inhabited 1000-1200 by people that are called 'ancestral pueblo' by the Park Service, since Anasazi is a Navajo term that can be translated as "invaders."
Anyway, the question always comes up, 'Why did they leave?" And the answer can be found in Jared Diamond's book Collapse. They outbred and outpopulated their ability to sustain themselves, stripping the land for miles around them.
I mention this because of my belief that the Anasazi were pretty much the way we are. People are people, in all times and all places. If we wonder why such and such a society did something, we need only ask, "What would we do in a similar situation?"
I mention this because there are people who simply will not accept the explanation that the Anasazi ruined their environment, because they were a non-industrial people, and, living in harmony with Mother nature, couldn't possibly have done bad things to Mom. I have news for those people: They could have and did. Living in harmony with nature means being hungry, diseased, and probably eaten. The "Harmony with nature" philosophy that you hear from Native Americans is probably a modern romanticism about their ancestors, who only wanted to live a little while longer, and probably paid as much attention to their religion as we do to ours. Which is to say, almost none.