[ZenGum]

We should distinguish between relative decline and absolute decline.
Relative decline considers the USA's position relative to other countries. In this measure I think most people would agree that the US is in relative decline, if only because of the extreme growth that China is going through. The US getting tangled up in foreign wars speeds the process.

For the US to decline in absolute terms would be to decay in terms of morale and national self-belief, which is where Rome first turned rotten. Lookout talks about the sort of things that cause this: (apparently) pointless wars, (perceived) social injustice, apathy.

My assessment: the US is at present the preeminent nation but China is rapidly overhauling them. In 20 or 30 years China will have more strength, but perceptions of US strength will continue beyond this - especially in the US. I doubt that the US will ever fall to the state where Spain is now - truly a bit-player. More like (sorry Lookout) France or Britain are today - still having some international credibility, but not dominating as now.

Say ... we're all watching China - has anyone been keeping an eye on India? They've got a billion people, the bomb, and a growing economy too. They may end up being the second player/balance to China.