(Arnd Wiegmann / Courtesy Reuters)

Playing a dominant role in world politics does not make for an easy life. Even very powerful states encounter problems they cannot solve and situations they would prefer to avoid. But as Macbeth remarks after seeing the witches, "Present fears are less than horrible imaginings." What really scares American foreign policy commentators is not any immediate frustration or danger but the prospect of longer-term decline.

Recently, the United States has been going through yet another bout of declinism -- the fifth wave in the last six decades, by the scholar Josef Joffe's count. This one has been caused by the juxtaposition of China's rising power and American economic, political, and military malaise. Just as in the past, however, the surge of pessimism has produced a countersurge of defensive optimism, with arguments put forward about the continued value and feasibility of U.S. global leadership.

Two examples of such antideclinist forays are Robert Kagan's The World America Made and Robert Lieber's Power and Willpower in the American Future. Both make some cogent points in their analyses of the past, present, and future of the existing U.S.-sponsored global order. But their authors' refusal to accord due weight to multilateral institutions and material power in their assessments of that order, and their overconfidence in making assertions about the future, reduce the books' value as appraisals of contemporary world politics.

IT TAKES AN INSTITUTION

Kagan's gracefully written essay notes that the United States has played an essential role in creating the international system of the last 60 years, one in which large-scale warfare has been relatively rare, the global economy has grown at unprecedented rates, and the number of democracies has quadrupled. Harking back to Frank Capra's It's a Wonderful Life, Kagan asks readers to imagine what the world would have been like during this period without American leadership and says the answer is clear: much less attractive. U.S. hegemony helped promote peace, prosperity, and political liberalization, and American power continues to be important in maintaining world order.

The World America Made offers a thoroughly conventional reading of world politics, one focusing on the sources and distribution of power in the international system and the ways in which states interpret their interests. The lack of a common government to enforce rules means that order depends on bargaining, which typically involves threats as well as promises. Threats imply some chance of conflict. And so international systems not dominated by a single great power have only rarely managed to sustain peace for long.

General readers might not realize how conventional this interpretation of world politics is, since Kagan strikes a pose of embattled iconoclasm, ignoring most of the major authors who developed the case -- such as E. H. Carr, Hans Morgenthau, and Kenneth Waltz -- and claiming to refute other scholars with whom he supposedly disagrees, such as G. John Ikenberry and Joseph Nye.

Unfortunately, Kagan's method of disagreement is unconvincing. When he raises an opposing claim, he almost never provides data or even systematic evidence; instead, he relies on a counterassertion with a few carefully selected examples. More annoying, he typically overstates the argument in question, stripping it of its original nuance, before claiming to refute it.

One of his favorite rhetorical tactics is to assert that his opponents think some trend is "inevitable" or "irreversible" -- the dominance of the American-led liberal order, the rise of democracy, the end of major war. Another is to suggest that his targets believe in "multipolar harmony." But two of the most basic propositions of contemporary international relations, certainly accepted by all the writers he dismisses, are that world politics is a realm of inherent uncertainty and that it is characterized by a natural absence of harmony. Since practically everybody knows that nothing in world politics is inevitable and harmony is virtually nonexistent, attributing the opposite beliefs to one's opponents assures one of victory in a mock combat.

It is precisely because international discord is the norm, in fact, that theorists and practitioners spend so much time and effort trying to figure out how to generate and sustain cooperation. Many well-informed commentators view the multilateral institutions that have emerged from all this work as providing important supports for the contemporary world order. They point to the roles of UN peacekeeping operations in fostering security, the World Bank in promoting development, the International Monetary Fund (IMF) in enhancing financial stability, the World Trade Organization in fostering commerce, and NATO and the European Union in helping achieve unprecedented peace and unity across an entire continent.

Kagan scoffs, arguing that other states accept U.S. dominance not because it has been embedded in such frameworks but because they approve of American values and goals and believe they may need American power down the road. He disparages the United Nations; ignores UN peacekeeping, the World Bank, and the IMF; and is dismissive of the European Union. But his rejection of the value of institutions is based largely on one sentence, worth quoting in full as an example of his style of argumentation: "All efforts to hand off the maintenance of order and security to an international body with greater authority than the nations within it, or to rely on nations to abide by international rules, regardless of their power to flout them, have failed." Yet Kagan does not mention the fact that the UN Security Council has always operated with the possibility of vetoes by any of the five permanent members -- showing that there was never any effort to endow it with authority above those states -- nor does he note the extensive literature that explores how states use the UN and other multilateral institutions to pursue their interests, rather than "hand[ing] off" power to them. This is less serious debate than the tossing of cherry bombs at straw men.

The World America Made thus combines a conventional and often sensible analysis of world politics and modern U.S. foreign policy with tendentious criticism of supposedly competing arguments that few, if any, authors actually make. Kagan does not engage in serious analysis of how much military power the United States needs to maintain its central leadership role, in alliance with other democracies, in a stable world order, or of how what Nye has called "soft power" can contribute, in conjunction with "hard" material power, to U.S. influence.

Lieber's book largely agrees with Kagan's, arguing that "the maintenance of [the United States'] leading [international] role matters greatly. The alternative would . . . be a more disorderly and dangerous world." Power and Willpower in the American Future documents the many erroneous statements about American decline by commentators such as the historian Paul Kennedy (who argued in 1987 that the United States suffered from "imperial overstretch") and even Henry Kissinger (who wrote in 1961 that "the United States cannot afford another decline like that which has characterized the past decade and a half"). Lieber provides useful data on the relative economic production of major countries and gives both his predecessors and his intellectual opponents due credit for their contributions.

In the end, however, the flaws in Lieber's arguments are similar to those in Kagan's. He, too, dismisses multilateralism as generally ineffective, emphasizing its failures while paying less attention to its successes, whether in peacekeeping, trade, or nonproliferation. He slights NATO's operations in Kosovo in 1999 and Libya in 2011, for example, arguing that the former exhibited "military and tactical limitations" and pointing out that "stronger and more decisive initial attacks" might have brought quicker success in the latter. Even if valid, surely these critiques are relatively minor compared to the results achieved, with high international legitimacy, in both cases. But Lieber has difficulty admitting that such episodes should be counted as evidence for multilateralism rather than against it.

In a previous book, Lieber offered a robust defense of and rationale for the foreign policy approach of the George W. Bush administration, including making a case for preventive war. One might have hoped that in this successor volume he would have revisited such issues and subjected the practical track record of unbridled unilateralism to the same sort of withering scrutiny he gives to multilateralism, but such self-reflection is not to be found here. (Nor is it present in Kagan's book, for that matter, where it would have been equally welcome.)

KNOWN AND UNKNOWN

Apart from questions of originality and the specifics of the declinist debate, the central problem with books of present-oriented foreign policy commentary such as these lies in their failure to distinguish between what is known and what is unknowable. By conflating the two, they end up misleading readers rather than educating them. It might be useful, therefore, to indicate half a dozen things relevant to the future of the U.S. global role that can now be said with confidence.

First, we know that in the absence of leadership, world politics suffers from collective action problems, as each state tries to shift the burdens of adjustment to change onto others. Without alliances or other institutions helping provide reassurance, uncertainty generates security dilemmas, with states eyeing one another suspiciously. So leadership is indeed essential in order to promote cooperation, which is in turn necessary to solve global problems ranging from war to climate change.

Second, we know that leadership is exercised most effectively by creating multilateral institutions that enable states to share responsibilities and burdens. Such institutions may not always succeed in their objectives or eliminate disagreements among their members, but they make cooperation easier and reduce the leader's burdens -- which is why policymakers in Washington and many other capitals have invested so much effort for so many decades in creating and maintaining them.

Third, we know that leadership is costly and states other than the leader have incentives to shirk their responsibilities. This means that the burdens borne by the leader are likely to increase over time and that without efforts to encourage sharing of the load, leadership may not be sustainable.

Fourth, we know that in a democracy such as the United States, most people pay relatively little attention to details of policy in general and foreign policy in particular. Pressures for benefits for voters at home -- in the form of welfare benefits and tax cuts -- compete with demands for military spending and especially nonmilitary foreign affairs spending. This means that in the absence of immediate threats, the public's willingness to invest in international leadership will tend to decline. (A corollary of this point is that advocates of international involvement have incentives to exaggerate threats in order to secure attention and resources.)

Fifth, we know that autocracies are fundamentally less stable than democracies. Lacking the rule of law and accepted procedures for leadership transitions, the former are subject to repeated internal political crises, even though these might play out beneath a unified and stable façade. China's leadership crisis during the spring of 2012, marked by the detention of the politician Bo Xilai and his wife, illustrated this point.

And sixth, we know that among democracies in the world today, only the United States has the material capacity and political unity to exercise consistent global leadership. It has shown a repeated ability to rebound from economic and political difficulties. The size, youth, and diversity of its population; the stability and openness of its political institutions; and the incentives that its economic system creates for innovation mean that it remains the most creative society in the world. Yet it also has major problems -- along with intense domestic partisan conflict that prevents those problems from being resolved and that constitutes a major threat to its continued leadership abroad.

What we don't know, however, is at least as important. Will the major powers in the international system, most importantly China, maintain their social and political coherence and avoid civil war? Will the instabilities in the global economy exposed by the 2008 financial crisis be corrected or merely papered over and thus left to cause potential havoc down the road? Will ideologically driven regimes, such as the one in Iran, be prudent or reckless in their quest to develop or even use nuclear weapons, and will potentially threatened states, such as Israel, act prudently in response? Will the trend in recent decades toward greater global democratization be maintained, or will it give way to an antidemocratic reaction? And perhaps most important for the issues discussed here, can the United States as a society summon the political coherence and willpower to devise and implement a sustainable leadership strategy for the twenty-first century?

When it comes to netting out all these factors, declinists are pessimists and antideclinists are optimists. Both camps, however, tend to blend knowledge and speculation and to ground their conclusions more in mood and temperament than in systematic evidence or compelling logic, making it difficult to take their confident claims seriously. Scientists are careful to note the degree of uncertainty associated with their inferences; pundits should seek to follow their example. Given the mix of the known and the unknown, the safest conclusion for readers interested in the next era of world politics is probably the physicist Niels Bohr's injunction not to make predictions, especially about the future.