Since the time of Ur, 6,500 years ago, all civilizations have followed the same life-cycle. They are born of a gathering together of people with one or more common interests. For a time, there is struggle and, usually, a violent tumult while the strongest of those interested parties battle for dominance within the society.
Once it has been decided who shall lead, and once that leadership is relatively secure from usurpation, there will be a period of growth in which most or many of the citizens of that civilization will have some degree of prosperity, however that word is defined within the civilization.
But as time goes on, it becomes harder for an individual at a lower station in the civilization to elevate themselves to a higher level. This produces a higher level of unsocial and anti-social activities such as we would see in a criminal underworld.
As discontent and disillusionment grow amongst the lower ranks, there will be different reform movements that will give a bit here and there, enough to keep the rabble quiet, but no more than absolutely necessary. This also makes sure that those in power stay in power. Regardless of a party or person who supposedly leads the country, no government stays in power without powerful outsiders allowing it, and the longer they remain in power, the more powerful they get. Power becomes concentrated in the hands of a very few at the top which hold the greater weight of resources.
And, then, as happened with Mesopotamia, with Greece, with Macedonia, Egypt, Rome, and Britain, the civilization could simply no longer support the structure upon which is was built. Whether by violence, decay or evolution, the empire crumbles and collapses.
In our modern times, Britain was able to manage its collapse, breaking its fall and remaining a viable and productive nation, if drastically reduced in wealth and world influence. This was a tactic which other, previous empires had not taken and it led to huge voids of power and many years of internal and external warfare.
But I am not convinced that the empire in which we live today is an entirely American empire. Since World War II and the aftermath programs such as the Marshall Plan and others, the empire, though founded on American industrial might, has become increasingly a Westernized Capitalist Empire created by and for those control what we now call multinational corporations and international banking interests. The current recession starkly depicts the interdependence of the economic network that has been around for the past 60 years and has recently come to be called Globalization.
Although not all Western countries have the extreme concentration of wealth at the very pinnacle of society, they are all top heavy and all are becoming more so. Even the great liberal nations of Scandinavia are beginning to show signs of wobbling.
I do not believe that we shall, as some more left-wing authors insist, see the end of Capitalism with this latest crisis, but I do believe that it is the masticization of the cancer of the Capitalist tumor that has been growing unchecked for the past 60 years, and, if truth be known, probably much longer than that.
I often point out that Adam Smith was not a poor man. He was a landed, wealthy son of a Scottish attorney and aristocrat and, as most of his kind, he believed he had a right to remain so. The wealth of nations of which he wrote was not the wealth of the peasant or serf; it was the wealth of the proprietor those who had the God-given right to possess.
But we have seen it before - the rising and falling of empires - and we shall see it again.
This time, I think the end will come, rather than with explosions and gunshots, with the whimpers of terminally ill patient who moans in his bed as each day he grows weaker from the cancer within.
 For more information on my source for this, take a look at http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address=389x6195406