Power is an elusive concept. As the political scientist Hans Morgenthau wrote, “The concept of political power poses one of the most difficult and controversial problems of political science.” Understanding the nature of power has long been central to the study of international relations and to the work of the US Intelligence Community. The task is now all the more important and elusive, because the United States enjoys an unprecedented amount of economic, military, and technological might in comparison to other states. Yet it must exercise its power in a world not only of state-related constraints on that power, but also of transnational forces and non-state actors that act as competitors, qualifiers, constrainers, and, sometimes, enhancers of that power.

At the dawn of the 21st century, the concept of power is more important, and more debated. How to measure the power of the United States is fundamental to the major debates over US foreign policy. If, as the globe’s “unipolar power,” the United States has power beyond precedent, then its foreign policy problem is simplified, for friends and allies will have to follow it whether they like it or not, and would-be adversaries will be cowed by the prospect of that power.

If, on the other hand, de facto US power is less than sometimes assumed or less usable than hoped, then the United States may face the prospect that erstwhile allies and friends will, almost as a law of physics, want to see it taken down a peg. They will, if not “balance” against it, then at least sit on the fence in circumstances like Iraq. They will be inclined to view the United States’ travails with a certain Schadenfreude—happy to see the dominant power reduced to more normal size, though prepared to stand with the United States if it were seriously in trouble.

Ascertaining State Power

Measurements of power matter significantly in today’s US policy debates. If the United States is really the unipolar state, one that is preponderant almost beyond historical analogy, then its policy problem is simplified. Other states will have little choice but to follow it. They will be like Canada in the famous saying attributed to former Prime Minister Lester Pearson: “The United States is our best friend, whether we like it or not.” On the other hand, if the United States is less dominant, then a national security strategy based on preponderance—on the assumption that all the major powers will be on the United States’ side—may not hold true. What if other states begin to form themselves not with the United States but against it, or at least hedge their bets?

State power can be conceived at three levels: the level of resources or capabilities, also known as power-in-being, the level of power conversion through national processes, and the level of power in outcomes, by which we refer to a state’s tendency to prevail in particular circumstances. The starting point for thinking about—and developing metrics for—national power is to view states as “capability containers.” Yet those capabilities—demographic, economic, technological, and others—become manifest only through a process of conversion. States need to convert material resources, or economic prowess, into more usable instruments such as combat proficiency. In the end, however, what policy-makers care most about is not power as capability, or even power converted from national ethos, politics, and social cohesion. They care about power in outcomes. That third level of power is by far the most elusive, for it is contingent and relative. It depends on how the power manifests itself, and against whom the power is exercised.

The main categories used to identify the first level of state power, the level of capability, are gross domestic product (GDP), population, defense spending, and a less precise factor capturing innovation in technology. Using these estimates, power is summed as a percent of total global power, and fourteen states hold at least a one percent share. The United States is at the top of the power structure, though it is hardly an isolated and unilateral power. While the United States currently holds nearly a fifth of total global power, it is closely followed by the European Union, considered as a unified actor, and China, which each hold about 14 percent. India, moreover, holds about 9 percent, while Brazil, South Korea, and Russia each hold about 2 percent.

These numbers, though only estimates, suggest possible alliances that could match the power of the United States acting alone or with its traditional allies. Such a power assessment also examines the most likely locations for future conflict, based on six criteria. Projections indicate that Asia is by far the most dangerous region, with six of the eight most conflict-prone bilateral balances involving China. The assessment also indicates that by 2015, the level of US power will be closely threatened by China and India, while the European Union and all non-US members of the Group of Eight will experience a slow decline in power.

Converting Resources into Power

Carnegie scholar Ashley Tellis and his colleagues at RAND have recently offered a re-examination of the concept of “national power.” They began by assuming that a meticulous detailing of visible military assets is required to understand the true basis of national power. It also requires a scrutiny of such variables as the aptitude for innovation, the nature of social institutions, and the quality of the knowledge base. For Tellis and his colleagues, all of these factors influence a country’s capacity to produce the one element that is still fundamental to international politics—effective military power.

Their core argument is that national power is divided into three linked realms: natural resources, national performance, and military capabilities. The first realm encompasses the level of resources either available to, or produced by, a country. The second realm, national performance, is derived from the external pressures facing a country and the efficiency of its governing institutions and its society at large. The third realm, military capabilities, is understood in terms of operational proficiency or effectiveness. Military capability is produced as a result of both the strategic resources available to a military organization and its ability to convert those resources into effective, coercive power. These three realms taken together describe national power.