Right.
But these are different times as well, communications across the globe can be made with the blink of an eye, in this age "everything" is 10x faster. I'm not saying that the fall of the USA will be in 10 years, it will likely take more than half a century. If, let's say the USA falls in 2060, then the empire has existed for approximately 100 years.
Now, comparing that to earlier empires it is somewhat short, but taking into consideration that this is a new age as I mentioned, and "everything" is faster, then perhaps 100 yearss is quite enough for an empire in the world of today.