Here is a free article from the head of Stratfor concerning the globe entering a new era beyond the post-cold war era. It's pretty good, and covers the EU, US and China. He lists out the real problems and issues facing each of the powers, though you will notice he does omit some items concerning the United States. The two major ones I suspect individuals in this corner of the net will notice is the absence of acknowledging the absolute danger our unsustainable debt, the threat posed by a potential monetary collapse, our declining civil liberties and the issue with immigration.
The first two are items Stratfor has always been rather weak on. Their analysis of global events is excellent in my opinion but they have a blind spot when it comes to the United States and its economic and fiscal matters. However, Stratfor has, correctly in my opinion, outline some key fundamental reasons why the US wields so much geopolitical power. The issue now is will our very real problems overwhelm our natural advantages. Obviously Mr. Friedman, due to the omission in his analysis, would say yes while others on the manosphere would so the exact opposite. I am somewhere in the middle. My concern with our economic situation is less about our geopolitical power as much as it is our personal well being. I do not, for a second, think that the US would elect what Britain or the USSR chose to do when faced between maintaining their empires or sacrificing more of their peoples well beings.
As for the the declining civil liberties, Mr. Friedman has addressed the issue in the past and stated that one of his fears was that no power can remain a true republic and an imperial power, though two are mutually exclusive. I believe civil liberties are very important in the ability for a nation to project power as John Adams once said, and I am paraphrasing: "A nation's power is dependent on it's liberties of it's people. And the nation with the largest population with the most free people will be the most powerful." But at the same time even on the long term time frame of real politics the effects of declining civil liberties can take some time to be realized.
Lastly, as for immigration, while Mr. Friedman did not address the issue in this article, he has in the past. In fact, in his book, the Next 100 Years, he maintains that in the later half of this century that the issue of immigration will be the most important issue concerning the United States and it's ability to project power. The American Southwest has always been a borderland between Mexico and America. America currently occupies it now because it is far more powerful, both in wealth, military and population than it's southern neighbor and because of that we control the south west. This was not always the case in the past and it may not always be the case in the future. Mr. Friedman thinks that there is a real possibility of a secessionist movement or even a war between Mexico, which he thinks will become a potential rival, and the US if the issue of immigration and assimilation is not adequately addressed.
Either way, you may agree or disagree with some or all of his assessments but it is worth a quick read.