The Financial Times today (Stephens, Philip, “A Physicist’s Theory of the Transatlantic Relationship,” 14 December 2007):

The overarching geopolitical fact of coming decades is likely to be the relative decline of US power. The word relative is important. Measured by economic, technological and military might, America is likely to remain the pre-eminent nation during the first half of the present century and, perhaps, well beyond. But the US is already an insufficient as well as an indispensable power. As China, India and others rise, and Russia re-asserts itself, the US will become more dependent on the goodwill of others. How it responds to the shifts will in large degree shape the new international order — or disorder.

The image of the future in the minds of many is of a multipolar system, with power shared between two or three groups of nations. … Others — in the US as well as Europe — conjure up a world divided into two competing blocs: the liberal democracies on one side, the authoritarian capitalists, notably but not exclusively China and Russia, on the other. …

More probably we are on the cusp of an era of great power competition in which alliances and allegiances shift according to accidents of circumstance and geography. Those who like historical analogies could look back at the second half of the 19th century.

The problem with looking back at the second half of the Nineteenth Century is that we all know how that ended.