The funeral oration by, Pericles:
Then, again, our military training is in many respects superior to that of our adversaries. Our city is thrown open to the world, though and we never expel a foreigner and prevent him from seeing or learning anything of which the secret if revealed to an enemy might profit him. We rely not upon management or trickery, but upon our own hearts and hands. And in the matter of education, whereas they from early youth are always undergoing laborious exercises which are to make them brave, we live at ease, and yet are equally ready to face the perils which they face. And here is the proof: The Lacedaemonians come into Athenian territory not by themselves, but with their whole confederacy following; we go alone into a neighbor's country; and although our opponents are fighting for their homes and we on a foreign soil, we have seldom any difficulty in overcoming them. Our enemies have never yet felt our united strength, the care of a navy divides our attention, and on land we are obliged to send our own citizens everywhere. But they, if they meet and defeat a part of our army, are as proud as if they had routed us all, and when defeated they pretend to have been vanquished by us all.
Anyways, the US will always be at the top as long as internal rot doesn't take place. That is one of the surest ways to destroy great countries. And once internal rot has taken place then the 'barbarian hordes' can take care of the rest. However, if the people can rely on their true strengths (as PEricles states 'their hearts and hands') then nothing can really shake the resolute spirit of this nation. The onyl way to destroy the US is to have Americans destroy themselves (primarily by messing up their youth so much that they are, in essence, no longer 'American' at heart but only in citizenship. And there is a huge difference between an 'American' and an 'American citizen' that i shall not go into right now. Anyways, if the younger generations are made (taught?) to forget their true heritage, and to eschew hard work in favor of 'good feelings,' then that opens doors.
Anyways.
But the US will always be number one .....up and until the moment it decides not to be. And if that ever happens it will be the people themselves who make that decision. And as amazingly stupid as that decision would be it is quite possible. Rome fell long before the Barbarians came a-storming at their gates.
Our astronomical debt is a sure precursor of internal rot.