I don't want to steel dB's thunder but it's quite reassuring that theres someone more pessimistic than me:
Remember the trinity of power -
1. Hard Power (Military) Chessboard
2. Economic Power (Trade) Chessboard
3. Soft Power (Propaganda) Chessboard
Is the glass half full or is the glass half empty:
The fact remains that the US occupies a very peculiar position in world history (since 1945) - it has massive military muscle on that chessboard, it has significantly lowered the amount of capacity to influence the rest of the world to do what it wants in terms of trade and economics. And it has lost terrific advantage it did have on the 3rd chessboard.
Go get 3 pie charts -
One with the world population with the american slice in it.
One with the share of world GDP with the american slice in it.
One with the share of total defense spending with the american slice in it.
When you look at them you think, SHIT!!
Theres 4.5% of the worlds population, (not even one twentieth)
with 20% of the world product.
and 52% of the worlds defense expenditure.
My next question is how long into the 21st century do you think that this can go on? - somewhere along that timeline theres going to have to come a massive convergence - and I don't think it's going to be a massive increase in population!