This is discussed in Jared Diamond's book "Collapse." (A good book, although winding.) A skewed sex-ratio was definitely one of the factors, but it would be foo

This is discussed in Jared Diamond's book "Collapse." (A good book, although winding.) A skewed sex-ratio was definitely one of the factors, but it would be foolish to say it was the only one. In fact, one of the theses of "Collapse" is that it is almost always a combination of multiple factors that leads to major changes in a society.