the main thing is
the fate of euro.
Who's the biggest enemy of the US?
terroists?
No they are too small and too weak.
China?
No, time is too early. China is not qualified yet.
The answer is: Euro.
American may have bigger debt in amount, but American is much stronger. Now, I guess, America has to force euro to print as much money as American QEs. We shall see how much euro printed in the next 2 years.