ARROYO GRANDE, Calif. (MarketWatch) -- "One of the disturbing facts of history is that so many civilizations collapse," warns anthropologist Jared Diamond in "Collapse: How Societies Choose to Fail or Succeed." Many "civilizations share a sharp curve of decline. Indeed, a society's demise may begin only a decade or two after it reaches its peak population, wealth and power." Now, Harvard's Niall Ferguson, one of the world's leading financial historians, echoes Diamond's warning: "Imperial collapse may come much more suddenly than many historians imagine. A combination of fiscal deficits and military overstretch suggests that the United States may be the...