When the world's only superpower gets weighed down with this much debt - to itself and other nations - everyone will feel it. How? Hard to predict. But all I know is that the most unique and important feature of U.S. foreign policy over the last century has been the degree to which America's diplomats and naval, air and ground forces provided global public goods - from open seas to open trade and from containment to counterterrorism - that benefited many others besides us. U.S. power has been the key force maintaining global stability, and providing global governance, for the last 70 years. That role will not disappear, but it will almost certainly shrink.

Great powers have retrenched before: Britain for instance. But, as Mandelbaum notes, "When Britain could no longer provide global governance, the United States stepped in to replace it. No country now stands ready to replace the United States, so the loss to international peace and prosperity has the potential to be greater as America pulls back than when Britain did."

After all, Europe is rich but wimpy. China is rich nationally but still dirt poor on a per capita basis and, therefore, will be compelled to remain focused inwardly and regionally. Russia, drunk on oil, can cause trouble but not project power. "Therefore, the world will be a more disorderly and dangerous place," Mandelbaum predicts.

How to mitigate this trend? Mandelbaum argues for three things: First, we need to get ourselves back on a sustainable path to economic growth and reindustrialization, with whatever sacrifices, hard work and political consensus that requires. Second, we need to set priorities. We have enjoyed a century in which we could have, in foreign policy terms, both what is vital and what is desirable. For instance, I presume that with infinite men and money we can succeed in Afghanistan. But is it vital? I am sure it is desirable, but vital? Finally, we need to shore up our balance sheet and weaken that of our enemies, and the best way to do that in one move is with a much higher gasoline tax.

America is about to learn a very hard lesson: You can borrow your way to prosperity over the short run but not to geopolitical power over the long run. That requires a real and growing economic engine. And, for us, the short run is now over. There was a time when thinking seriously about American foreign policy did not require thinking seriously about economic policy. That time is also over.

An America in hock will have no hawks - or at least none that anyone will take seriously.

David Fuller's view A Fullermoney theme over the last decade is that is a rapid and irreversible global change is occuring as we move from a unipolar to a multipolar world. If this means more soft (diplomatic) power from the USA and more involvement from other democracies, the world could be better off for it. The biggest uncertainties are likely to concern authoritarian regimes. Commodity producers will have more financial power and we are likely to see more competition for scarce resources.