^ there is a major flaw in your logic above, you are assuming that China, India and those export countries could survive on their own. If the export stops, then they will collapse, so much for an empire. They become "powerful" because we exported our power, but a few decades of export is insufficient to maintain that power when we stop feeding them. China collapse will happen before the US because they still remain inherently fragile and their growth is based on "superficial" goods.
also, you can't compare the current situation with the past. There is one major factor that didn't exist in the past: worldwide instant communication. Because of this, economic factors adjust much more rapidly and become inter-indepedent, there is no one empire fighting many countries, but ONE global country made of little Empires. Things have changed, and extrapolling history without taking into account a significant fundamental change in the landscape is a bit foolish in my opinion. The 20th century is a turning point in our civilization, like the 11th century and Renaissance have been previously.