Impotent power? Re-examining the nature of America's hegemonic power.

• Author: Layne, Christopher

DURING THE last several years it seems as if every major book or article on American grand strategy contains the observation that the United States is more powerful than any international actor since the Roman Empire was at its zenith. At the same time, however, the U.S. failures to suppress the insurgency in Iraq and to stabilize Afghanistan have caused many foreign policy analysts to ask, "Why is it that the United States with all its hegemonic power cannot seem to get its way and attain its objectives in places like Iraq and Afghanistan, and in its disputes with powers like Iran and North Korea?"

There is a paradox between the magnitude of American power and Washington's inability to use that power to always get what it wants in international politics. There are many factors that limit the exercise of U.S. power. Some of these are obvious, others less so.

By all accepted measures the United States is an extraordinarily powerful global actor. The United States dominates the global economy with a Gross Domestic Product (GDP) of about $11 trillion. China, usually cited as America's most likely future great power rival, has a GDP of approximately $1.4 trillion. Not only is the U.S. economy big, it is also at the forefront technologically. The dollar remains the primary reserve currency for the international economic system--a huge advantage for the United States, since other nations keep propping up the dollar for fear that a major drop in its value would negatively affect their own investment portfolios. U.S. economic power is also reflected in Washington's dominance of key international economic institutions such as the World Bank and International Monetary Fund.

Economic strength and technological prowess go a long way toward explaining America's military dominance. The sheer magnitude of the U.S. economy means that Washington is easily able to spend over $500 billion annually on defense. This is more than the rest of the world combined spends on defense, but only about 4 percent of the U.S. GDP, which means that even at this enormous absolute level of expenditure, defense spending is far less of a burden on the American economy than was the case during the Cold War.

The United States, indeed, is a global hegemon and has formidable tools at its disposal, and it can wield its power effectively to attain important policy objectives. For example, the sheer magnitude of America's lead in military power over its closest would-be rivals has a potent effect in dissuading them from trying to emerge as great powers and to challenge the United States's dominant role in a unipolar world. Events since 9/11 have illuminated other ways in which the United States has been able to utilize its hegemonic power. Thus, American military prowess was showcased by the quick collapse of the Taliban and Saddam's Iraq. Moreover, the economic incentives the United States could proffer were vitally important in persuading a reluctant Pakistan to allow itself to ally with the United States in the battle against Al-Qaeda. Central Asian states offered the United States the opportunity to establish military bases--and Putin's Russia acquiesced to this. And the very fact that the United States could defy the United Nations (and major powers such as France, Germany, Russia and China) and carry out the invasion of Iraq (essentially) unilaterally proved--if proof is needed--that the rest of the world could not do much to constrain the United States.

But hegemony is not omnipotence. Back in the 1960s, Thomas C. Schelling made an important distinction in the purposes for which power could be used: He differentiated between deterrence and compellence.

Deterrence involves the use of power to persuade another state to refrain from taking an action that the United States does not want it to take. Compellence, on the other hand, involves the coercive use of American power to compel another state (or substate actors) to act, against its own preferences, in ways that Washington wants it to act.

The United States has had a high degree of success using its military power to deter other states from attacking the American homeland, or U.S. allies abroad, even though deterring terrorists is much harder than deterring states. It has been far less successful at compellence. This helps to explain, for example, why American military power stops North Korea and Iran from attacking their neighbors but is seemingly ineffective in persuading them to give up their nuclear weapons programs.

Viewed from this perspective, it is not a surprise that the United States is foundering today in the Iraqi morass and failing in Afghanistan. Occupying and pacifying another country once it has been defeated is a difficult task for two reasons. First, as the United States learned in Vietnam and now is learning again in Iraq...