All nations large and small, empires or otherwise, rise and fall. America is no exception. However, this collapse in not imminent in my opinion and the US is likely to outlive the lifespan of previous world powers.  Predictions of a total collapse are just wishful thinking for the most part. But, yes, a day will come, whether in  our lifetime or afterwards, when the balance of power in the world is bound to shift against the US because of the reaction of people around the world to overt and covert agression by the United States in the world arena. The invasion of Iraq and Afghanistan, regardless of the outcome, has set in motion the wheels of America's decline in the world stage in my opinion. US leaders and diplomats may be able to slow down the decine, and I think they will, but in a world where more and more people are educated and empowered and demand dignity, equality and respect, the idea of one country dominating and projecting its will on others will not fly for long.

The irony of it all is demoracy may turn out to be biggest enemy of American power. If everyone in the world was as empowered and free as advocated in the rhetoric of US politicians, such free and empowered people will probably turn their ire against the US sooner or later.

As for the argument that anybody, given the opporunity, will want to live in the US - I don't buy that. That might have been true 20 or 30 years ago when an American lifestyle provided many material benefits that you could not find in other countries, but in this day and age, with the internet revolutionizing the way we interact with others and a globalized consumer-driven  economy delivering the latest goods and products to far-flung areas of the world, America has lost some of it's lusture to the kind of immigrants it supposedly wants  to attract -  educated and highly skilled workers. Of course, it will always attract the "tired, poor and huddled masses" from poorer regions like Mexico  (and Nepal) if that's who people are thinking about.

Just my thoughts.