Since the end of the cold war, American leaders have consistently claimed the ability to maintain a significant forward-leaning military presence in the three major regions of the globe and, if necessary, to wage two major regional wars at the same time. The harsh reality is that the United States no longer has the economic capacity for such an ambitious grand strategy. With 30 percent of the world's product, the United States could imagine maintaining this hope. Nearing 20 percent, it cannot.

Yet, just withdrawing American troops from Iraq is not enough to put America's grand strategy into balance. Even assuming a fairly quick and problem-free drawdown, the risks of instability in Iraq, Afghanistan and elsewhere in the region are likely to remain for many years to come. Further, even under the most optimistic scenarios, America is likely to remain dependent on imported oil for decades. Together, these factors point toward the Persian Gulf remaining the most important region in American grand strategy.

So, as Europe and Asia continue to be low-order priorities, Washington must think creatively and look for opportunities to make strategic trades. America needs to share the burden of regional security with its allies and continue to draw down our troop levels in Europe and Asia, even considering the attendant risks. The days when the United States could effectively solve the security problems of its allies in these regions almost on its own are coming to an end. True, spreading defense burdens more equally will not be easy and will be fraught with its own costs and risks. However, this is simply part of the price of America's declining relative power.

The key principle is for America to gain international support among regional powers like Russia and China for its vital national-security objectives by adjusting less important U.S. policies. For instance, Russia may well do more to discourage Iran's nuclear program in return for less U.S. pressure to expand NATO to its borders.

And of course America needs to develop a plan to reinvigorate the competitiveness of its economy. Recently, Harvard's Michael Porter issued an economic blueprint to renew America's environment for innovation. The heart of his plan is to remove the obstacles to increasing investment in science and technology. A combination of targeted tax, fiscal and education policies to stimulate more productive investment over the long haul is a sensible domestic component to America's new grand strategy. But it would be misguided to assume that the United States could easily regain its previously dominant economic position, since the world will likely remain globally competitive.

To justify postponing this restructuring of its grand strategy, America would need a firm expectation of high rates of economic growth over the next several years. There is no sign of such a burst on the horizon. Misguided efforts to extract more security from a declining economic base only divert potential resources from investment in the economy, trapping the state in an ever-worsening strategic dilemma. This approach has done little for great powers in the past, and America will likely be no exception when it comes to the inevitable costs of desperate policy making.

The United States is not just declining. Unipolarity is becoming obsolete, other states are rising to counter American power and the United States is losing much of its strategic freedom. Washington must adopt more realistic foreign commitments.

SINCE 2000, a systemic change has been occurring in the economic foundations of America's relative power, and it may fall even further in the foreseeable future. None of the dramatic consequences for U.S. grand strategy is likely to be immediate, but neither are those effects easily avoidable. For nearly two decades, the United States has experienced tremendous latitude in how it chooses to conduct itself in the world. But that latitude is now shrinking, and American policy makers must face facts. With the right grand strategy, however, America can mitigate the consequences of its relative decline, and possibly even reverse it.

Robert A. Pape is a professor of political science at the University of Chicago.

The author would like to thank Felicity Bloom, Daragh Grant, Jacob Homan, Chaim Kaufmann, Nuno Monteiro and especially Ken Feldman.

¹ For excellent discussions of the concept of power, see John Mearsheimer, The Tragedy of Great Power Politics (New York: W. W. Norton, 2001), ch. 3; and Edward Vose Gulick, Europe's Classical Balance of Power (New York: W. W. Norton, 1955), ch 1.

² Stephen G. Brooks and William C. Wohlforth, World Out of Balance: International Relations and the Challenge of American Primacy (Princeton, NJ: Princeton University Press, 2008), 32.

³ For explanations of different measures of gross domestic product, see glossaries for the International Monetary Fund, "World Economic Outlook Database" (October 2008) and World Bank, "World Development Indicators" (2008), both available online.

⁴ For a classic study of the diffusion of technology in past eras, see David S. Landes, The Unbound Prometheus: Technological Change and Industrial Development in Western Europe from 1750 to Present (New York: Cambridge University Press, 1969).        
⁵ See the Global Market Information Database; CIA World Factbook for the above dates; the National Science Board's "Science and Engineering Indicators 2008"; Nationmaster.com; and International Telecommunication Union's "International Communication Statistics, 2007." All were accessed online from August to October 2008.

⁶ This counterfactual calculation and the one in the next paragraph rely on the current-dollar method preferred by the unipolar-dominance school.

⁷ Richard K. Betts, Nuclear Blackmail and Nuclear Balance (Washington, DC: Brookings Institution Press, 1987).

⁸ For instance, Richard Bernstein and Ross H. Munro, The Coming Conflict with China (New York: Alfred A. Knopf, 1997).