Great powers, like great men, are born, rise, reign and then gradually wane

"The challenges that face the United States are often represented as slow-burning. It is the steady march of demographics -- which is driving up the ratio of retirees to workers -- not bad policy that condemns the public finances of the United States to sink deeper into the red.
It is the inexorable growth of China's economy, not American stagnation, that will make the gross domestic product of the People's Republic larger than that of the United States by 2027. "

I like to compare Nations to families, abstract entities to real people, because a Nation is nothing else than the families and the people who make it.
Usually the children of a rich, well established family don’t do well, used to luxury and comforts, while a child from a poor family is more motivated and in spite of all difficulties will succeed better that the other.
Survival need which includes the dream of a better life is often the reason why Nations like China can do much better than USA.
When you have more than what you need, that is the moment you stop working.
When it is easier letting THE OTHERS produce and just resell, that is the moment in which your economy begins dying.

After the Second World War the Americans thought:
"Let's be fair. We have been Top Nation for long.
We have done splendidly well once again.
Now we must give others a chance: let's decline."
But it is not so easy to decline.
After a few centuries other nations just will not believe that you are as inefficient and couldn't care less as you are.
They will insist on thinking of you as succesful, reliable and rich, however unsuccesful, unreliable and poor you may have become.
It needs the unfailing effort of rich and poor, old and young, intellectual and illiterate, skilled and unskilled.
It is an arduous, almost herculean task, but nothing will deter the
Americans, once they have made up their minds.
They played a great part in destroying Nazi Germany; the destruction of democratic America seems child's play compared with that.
The general strategy is grandiose: let us give away our Empire as fast as possible or a little faster; let us ruin the dollar by pretending that we did not give away our Empire and can still be a reserve currency; let us distribute overseas aid in a grand manner, at the same time, let us go around begging for oil.
Made in USA used to be synonymous with quality, so let us not rest until it means "shoddy goods, delivered late (how could it be different, it comes from China).
All this needs great determination, skill and the united effort of a great nation.
But the Americans aren't the Americans for nothing.
To their eternal glory, they are on the way to complete success.