Complexity has a cost in physical energy, administrative friction and other forms. At first, increases in complexity seem affordable and even useful. Eventually, however, a law of diminishing marginal returns on complexity sets in, and the costs, while difficult to see, become harder to bear. If such a complex society is then buffeted by external or internal shocks, it can collapse. The shocks have typically included droughts, famines, plagues, migrations, rebellions, civil wars and invasions
In 2005, I read the books, Collapse: How Societies Choose To Fail or Succeed by Jared Diamond (who was all over public TV with Guns, Germs and Steel) and A Short History of Progress by Ronald Wright. I found them fairly similar in theme, both dealing with Easter Island and other collapsed societies.