Gald you asked Oregonian! It is cyclical, and has been demonstrated by co-authors Strauss & Howe in the book The Fourth Turning. As a matter of fact, western society has followed this pattern of boom and bust with human generational lines drawn at about twenty to twenty five year intervals.

Here's the best part - based on observation of historical patterns, Strauss & Howe predicted great turmoil early in the 21st century and stated it could be caused by terrorists flying planes into buildings or landmarks, or a financial catastrophe like the great depression. The book was published in 1996 or 1997. They proposed other scenarios as well, but it was striking that they included those two and it has come to pass. The good news historically is that we have always pulled out of the mess.