The conclusion that size matters may be incorrect from the standpoint of much political science, but it is well supported by Stephen G. Brooks and William C. Wohlforth in their book. Proponents of the three leading paradigms in international politics—realism, liberalism, and social constructivism—claim that the current American predominance in the international system should generate balancing dynamics that would restrain the United States. The authors dispute both the logic and the evidence that has been adduced in support of such claims and make the case so clearly that World out of Balance can be used in upper-division undergraduate courses and also read with profit by members of the profession. It will stand as a major book for years to come.

It is almost beyond dispute that the situation that has prevailed since the end of the Cold War is unprecedented as to the unequal distribution of power in the international system. But, as the authors note, the common understanding of most theories is that the United States will be quite restrained by the actions or anticipated reactions of others. Disputing this is their signal contribution. Many realists have argued that as the most powerful state in the system, the United States will be the target of counterbalancing, if not by traditional alliances then by what has become known as “soft balancing”—that is, a variety of measures to increase states' individual and collective powers and hinder the ability of America to act on its own. Not so, the authors argue. First, the logic of balance of power applies only to the attempt to prevent a state from gaining a position of dominance. If and when a state has succeeded in establishing itself, as the United States did when the Soviet Union collapsed, it is likely to be strong enough so that attempts to unseat it, or even to block it when it feels strongly, will be unattractive.

Indeed, when we look at history since the end of the Cold War, and even since the invasion of Iraq, we do not see balancing, either hard or soft. This is not to say that states always cooperate with the United States, but that when they do not, the reasons are domestic politics, intraregional concerns, the belief that the country is acting foolishly, and the play of normal international frictions. There is no concerted effort to cut the United States down to size—it is simply too big for that.

In parallel, the common interpretation of liberalism postulates two different dynamics that might restrain the United States. The first is economic interdependence. But the authors again point to the basic asymmetries produced by size: The country is much less dependent on others (and especially on any individual country) than others are on it. While the authors are convincing on these points, perhaps more important is the argument that the United States will be restrained by the belief that excessive assertiveness and the failure to sufficiently provide public goods will weaken the international economic system and harm its own prosperity, a topic they gloss over. The second mechanism liberals invoke is the influence of international institutions, which require each participant to maintain a reputation for living up to its word and acting constructively. Again the authors disagree. Reputations do not spill over from one issue area and institution to another, in part because observers look at the particular interests at stake. As someone who has worked on the issue of reputation, I would have liked a more detailed discussion with more evidence, but this area remains one that requires further work.

For constructivists, institutions are also important, but predominantly as conveyors of legitimacy. The restraint on the sole superpower seen by these theorists is that inappropriate actions will lack legitimacy, either because of the way they have been developed (e.g., without approval of the Security Council or other relevant body) or because they violate accepted norms. Brooks and Wohlforth argue that here, too, the size of the United States undermines this claim. Its diverse resources often add to its legitimacy, and it is well positioned to deploy the very tools that constructivists stress—rulemaking, carving out exceptions to undesired rules, and mitigating legitimacy costs by providing side payments and public goods. Furthermore, in spite of the almost unanimous agreement among scholars and pundits that American actions in Iraq and the war on terror have undermined American legitimacy, it is hard to show that this has produced restraints that have ensnared the country or that will guide it back into more appropriate behavior.

It is important to note that Brooks and Wohlforth are not arguing that recent history has disconfirmed the dominant theories. Rather, they are making the more interesting point that scholars have misinterpreted their own theories in claiming that these imply that there are major external restraints on the sole superpower. Although they do not delve into the sources of the error, the obvious explanation is that most scholars disapprove of current American behavior and would like to believe that their theories indicate not only that it should not but also that it cannot be sustained.

All this could be read as a defense of the Bush Doctrine, but it is not. Brooks and Wohlforth are not arguing that this policy has been wise, but only that it has not led to the rise in external restraints on the United States. Indeed, they argue, the scholarly concentration on the supposedly systemic constraints on U.S. power has diverted attention from other restraints, such as proliferation, terrorism, insurgency, and imperial overstretch. While the substance of their brief discussion is to the point (pp. 208–13), the claim that these factors have received little attention is an exaggeration.

Entire articles, if not books, will be written in response to this book. I would just note that the authors say too little about the domestic restraints on the use of domestic power (pp. 5–6), do not address the fundability of power, and do not deal with the question of the extent to which American behavior and even preferences are shaped by interdependence and the desire to minimize opposition. Even more, difficulties are created by the fact—if it is a fact—that what the United States wants is not only security and influence but also the establishment of democracies around the world, which, it believes, will lead to a system characterized by common values and the ability to solve common problems. Even if others cannot restrain the United States by actively opposing it, such a world may remain beyond the American reach, and seeking to gain it may impose costs on the country as well as on others. At the end of their study, Brooks and Wohlforth imply that such an effort to promote democracy American style, led more wisely than President George W. Bush has done, might succeed. But it is a significant jump from arguing that others cannot restrain the United States to concluding that America can reshape world politics as it pleases.