I loved Guns, Germs, and Steel by Jared Diamond so I have been looking forward to reading Collapse and I finally got around to it. It was a fascinating read. My world view was altered more by the former book but this was still quite enlightening.
The primary focus of this book is how the environment and climate and our interactions with the natural world are major factors in the reason that societies fall apart. For example, if your society is heavily reliant on just the right amount of rainfall to keep everyone fed then a few years of bad drought could be enough to bring your society down.
The book is wide ranging in the societies that are studied both ones that did collapse and that did not. We find that we are not necessarily beholden to collapse simply because certain environmental conditions are untenable. The Greenland Inuit versus the Greenland Norse provide one example, with the Dominican Republic compared to Haiti being another.
We have a significant impact on the environment and I was left somewhat pessimistic by the book. It was written 10 years ago and although he said he was cautiously optimistic, I feel that things have mostly gotten worse.
I highly recommend this book and his previous one. I am definitely going to put Upheaval on my list as it represents the third book in a sort of trilogy on the subject of the rise and fall of civilizations.