Newsweek:"Is America's Dominance Waning?"

The answer to the question is yes. America under decades of incompetent leadership has overstretched itself militarily without the resources to support that empire:

With hindsight, we may see 2006 as the end of Pax Americana[...]the United States increasingly lacks both the power and the will to play this role. It isn't just Iraq, though Iraq has been profoundly destabilizing and demoralizing. Many other factors erode U.S. power: China's rise; probable nuclear proliferation; shrinking support for open trade; higher spending for Social Security and Medicare that squeezes the military, and the weakness of traditional U.S. allies, Europe and Japan.

Are we really all that powerful?:

The trouble is that strength—measurable and impressive—does not translate directly into power. Power is the ability to get others to do what you want. Here, America is weaker.

China is getting stronger while we get weaker:

China's emergence is altering the world balance. In spirit, its economic policies are mercantilist. It subsidizes its exports with an artificially low exchange rate; it is seeking captive oil supplies. China's policies are for China, not a stable world order.

September 11th and subsequent events have showed America's weakness, not strength. The world no longer fears us. And that will invite more aggression. The Pax Americana is over.