But there are times when even he must admit that global hegemony isn’t cheap. For one thing, in inflation-adjusted dollars, the base military budget for 2012, $531 billion (excluding the cost of the wars), exceeds the average annual level of Pentagon spending during Ronald Reagan’s eight years in office, $524 billion, and is well above the post–Cold War average of $452 billion. When confronted with such facts, Kagan reverts to a different sort of argument; maintaining our current posture might be costly, he avers, but the likely alternative world that would emerge after U.S. retrenchment would be costlier still.

Indeed, if Kagan were to have his way, the United States likely would spend even more on its military than it has over the past two decades. How much more? We can’t know for certain, but he is advising Mitt Romney, who has pledged to spend at least 4 percent of GDP on the Pentagon’s base budget, plus whatever more is needed to fight the occasional wars. According to my calculations based on five-year defense plans and ten-year OMB projections, Romney’s budget would result in $2.5 trillion in additional spending over the next ten years. Military spending, pegged to 4 percent of GDP in 2022, would top $1 trillion, 60 percent higher than under President Obama’s latest budget projections.

Kagan is correct to point out that the defense budget didn’t cause the deficit and that cutting the defense budget wouldn’t cure it. But he goes too far when he argues that military spending is all but irrelevant to the nation’s fiscal crisis. U.S. military spending, including war costs, officially peaked in 2010 at $690.9 billion. A more complete accounting of all security-related spending in that same year, including the Departments of Homeland Security and Veterans Affairs, totaled above $800 billion, or 23 percent of total federal spending—hardly an insignificant share.

But it is the vast disparity between what Americans spend and what others spend, and the clear trends showing a widening gap between the two, that poses the greatest challenge to Kagan’s world order. American hegemony isn’t economically unsustainable, but it might be politically unsustainable.

In Robert Kagan’s world, most of what Americans spend on the military isn’t intended for their defense but rather for the defense of others. It is no wonder, then, that most Americans are deeply dissatisfied with the present state of affairs. But the discontent goes deeper. Some Americans are fearful of global trade or suspicious of foreigners who would come to the United States to “steal” American jobs. Kagan, to his credit, is an advocate for global trade and is anxious to turn back the xenophobia and bigotry that drive some Americans to want to cut off all access to the outside world. Other aspects of this backlash against U.S. foreign policy are driven by a lack of understanding of the issues and confusion around some basic facts—for example, the widespread though mistaken belief that foreign aid constitutes a large share of the federal budget.

Correcting these misperceptions is, or at least should be, a central goal for a public intellectual. When presented with the facts, however, Americans grow less supportive of Kagan’s foreign policies. For example, while foreign aid in the form of direct payments to foreign governments or NGOs is often counterproductive, the sums are relatively small. Accordingly, people’s attention is now shifting to how our massive military budget acts as a different form of foreign aid: the security guarantees we dispense to wealthy, stable democracies have allowed them to avoid paying for their own security.

Meanwhile, the greatest threats to the nation’s long-term fiscal outlook are rising health-care costs, entitlements and other mandatory spending, but Kagan doesn’t spell out how to mobilize the political will to cut from these programs in order to cover the price of a larger and more costly military. When he argues that Americans could choose to forego the benefits that now three generations have come to expect as a birthright, he is looking past present-day political reality. And his contention that Americans should be willing to do so in order to ensure that people in other countries can continue to enjoy even more generous retirement benefits defies common sense.

IDEAS HAVE Consequences, declared the title of a 1948 book by the conservative writer Richard M. Weaver. Not so, says Robert Kagan in 2012: “The better idea doesn’t have to win just because it is a better idea. It requires great powers to champion it.” Likewise, the liberal order, he predicts, “will last only as long as those who imposed it retain the capacity to defend it.” Near the end of The World America Made, the man who is so quick to celebrate America’s many virtues reduces them down to just one that matters:

What has made the United States most attractive to much of the world has not been its culture, its wisdom, or even its ideals alone. At times these have played a part; at times they have been irrelevant. More consistent has been the attraction of America’s power, the manner in which it uses it, and the ends for which it has been used.

On the surface, this is a curious assertion for someone who seems to revel in ideology, particularly one who professes such faith in the transformative power of democracy. Kagan’s writings over the years, including The World America Made, amount to a full-throated endorsement of democratic-peace theory.

In other respects, however, Kagan’s dismissal of ideas and ideology is consistent with another recurring theme in his work: the utter disdain for an American foreign policy that leads by example. Ronald Reagan famously, and often, spoke of America as a shining city on a hill. The mere suggestion elicits scorn from Kagan.

In a telling passage from a 1996 article entitled, ironically enough, “Toward a Neo-Reaganite Foreign Policy,” Kagan and William Kristol savaged John Quincy Adams’s suggestion that America ought not go “abroad in search of monsters to destroy.” Kagan and Kristol declared:

Because America has the capacity to contain or destroy many of the world’s monsters, most of which can be found without much searching, and because the responsibility for the peace and security of the international order rests so heavily on America’s shoulders, a policy of sitting atop a hill and leading by example becomes in practice a policy of cowardice and dishonor.

Kagan returns to both this theme and Adams’s quote in The World America Made. America’s conception of itself as the reluctant sheriff, unwilling to go out in search of trouble but willing to defend the town only when called upon, “bears no relation to reality,” he explains. “Americans have used force dozens of times, and rarely because they had no choice.”

But the world is too complex to be policed by a single global sheriff, and it need not be. Instead, the many beneficiaries of the current order should contribute to the preservation of that order at a level, and in a manner, that is consistent with their interests. By that standard, the United States would retain military power that was at least three or four times greater than that of its closest rivals, but it would no longer presume to be responsible for countries that can take care of themselves.

Americans must learn to embrace their relative security and face down their lingering fears. Until they do so, the fear of the unknown works in Kagan’s favor. It is difficult to disentangle the many different factors that have contributed to relative peace and security over the past half century, and it is impossible to know what would have happened in a world without America. The future is even more inscrutable. In this latest book, Kagan surveys all the explanations for what may have contributed to global peace and prosperity—including the spread of democracy, liberal economics, nuclear weapons, and evolving global norms against violence and war—and returns to his refrain from sixteen years earlier. “American hegemony,” he and Kristol wrote in 1996, “is the only reliable defense against a breakdown of peace and international order.” Fast-forward to 2012, and nothing, it seems, has changed:

There can be no world order without power to preserve it, to shape its norms, uphold its institutions, defend the sinews of its economic system, and keep the peace. . . . If the United States begins to look like a less reliable defender of the present order, that order will begin to unravel.

He didn’t prove that case before, and he doesn’t now.

Christopher Preble is the vice president for defense and foreign-policy studies at the Cato Institute.

Pullquote: The world is more complicated and durable than Kagan imagines. The United States does not need to police the globe in order to maintain a level of security that prior generations would envy.Image: Essay Types: Book Review