America is in decline but the 'fall' is a long way away. We'll all be long gone before that happens.
American hegemony will continue to recede over the next century and a half, both because of its debt problems as well as changes in ethnic demographics. The growing population of less educated and less educable minority groups, such as Hispanics, will result in a larger destitute American underclass that is unable to contribute to the nation economically, politically, and technologically. Debts will compound, States will be bankrupted, and technological competitiveness will be compromised or surpassed by other nations.
Developing nations will reach relative parity with the West and each country will have its own small powerful wealthy elites that wield all power while the average joe in every society returns to the peasantry of his forefathers. Globalization will be complete.