This info graphic is very telling.  It is from the recent IMF forecast reported here:

http://www.marketwatch.com/story/imf-bombshell-age-of-america-about-to-end-2011-04-25?dist=countdown

It seems I’ve heard this before in history class.  The following excerpted from Wikipedia:

In The History of the Decline and Fall of the Roman Empire (1776–88), Edward Gibbon famously placed the blame on a loss of civic virtue among the Roman citizens. They gradually entrusted the role of defending the Empire to barbarian mercenaries who eventually turned on them. Gibbon held that Christianity contributed to this shift by making the populace less interested in the worldly here-and-now because it was willing to wait for the rewards of heaven. "The decline of Rome was the natural and inevitable effect of immoderate greatness. Prosperity ripened the principle of decay; the causes of destruction multiplied with the extent of conquest; and as soon as time or accident had removed the artificial supports, the stupendous fabric yielded to the pressure of its own weight," he wrote. "In discussing Barbarism and Christianity I have actually been discussing the Fall of Rome."

(source: http://en.wikipedia.org/wiki/Decline_of_the_Roman_Empire)