You may very well be right about that. The really important question is whether we can engineer a "soft decline" rather than a "hard fall". Neither is inevitable. The Portugese, Spanish, and British empires are all what I would consider to be examples of empires that had a soft decline. Rome, of course, is the classic example of a hard fall, but there are others as well.
You need to update your world view. The world is one e-mail, phone call and a 15 hour plane ride away from any point.
There are no empires in a geopolitical sense. America is an empire of blessed spirit, inspired engineering and irresistable and timeless human lure. That's unassailable.