So-called 'trend growth' has been fueled by fossil fuels, with massive increases in the ability to exploit oil fields quickly, occurring since the 40's.

Basically, civilization is a heat engine, where prosperity, power, industry is directly tied to how much energy we can burn. Increasing prosperity demands increasing energy.

In the case of the US, oil production peaked in 70's, and the US has struggled to increase oil supplies since then. The show-downs with OPEC in the 70's that led to bad recessions are an example of the struggles.

As of 2005, World oil production has been basically flat. There's plenty of oil left, the problem is that despite trillions of dollars of CAPEX, it just can't be pumped fast enough to support 6 billion humans at increasing living standards.

Hence, World prosperity is probably staying level, but redistributing itself Eastward towards Asia.

edit: Per NBC, there are 45 million Americans claiming foodstamps in order to feed themselves. That's a very scary contrast with how the US normally thinks of itself.