Moisés Naím / Foreign Policy

The terrorists that crashed jetliners into the World Trade Center and the Pentagon not only killed people. They also killed ideas, shattering the certainties that previously guided policies and budgets. Some of the ideas that died on that Tuesday morning in September had been with us for decades. Others were as new as the Bush administration. In their place has come not just the revival of some useful old truths but the emergence of new assumptions and perceptions that may be as dangerous as those that have been discarded.

Foremost among the ideas killed by the terrorists was the notion that technology could make the American homeland impregnable. We don’t know if the demise of this idea will also kill plans for a missile shield to protect the United States from intercontinental ballistic attacks by "rogue states." For some, National Missile Defense (NMD) is religion, not policy. And for many others, there is too much money to be made and too many careers at stake for this program to die. Certainly, proponents will have a much tougher time persuading Americans that NMD represents the best possible use of their tax dollars.

In any case, the idea that military superiority buys national security is now gone, too. The terrorists made everyone fully and painfully aware of the concrete meaning of "asymmetric war": enemies that respond to high-tech weapons with low-tech tools. In other words, box cutters against satellites. The idea that, in some instances, the brilliance of scientists and engineers is no match for the suicidal motivation of fanatics is now a conviction burned into the minds of all who saw the harrowing scenes of planes smashing through the twin towers.

The attacks have also sparked two new and very problematic ideas. The first is that the fight against terrorism is a "war" and therefore can be "won." The second is that the other foreign policy problems that confronted the United States before September 11, 2001, can be put on the back burner while the war against terrorism is waged.

The devotion of more attention and money to efforts to prevent and fight terrorism is long overdue. But terrorism has always existed and will not be eradicated. In fact, by boosting the terrorists’ mobility, agility, and reach, globalization has made them much tougher adversaries. Moreover, the world does not lack fertile breeding grounds for future terrorists. The idea that the elimination of Osama bin Laden and his network will substantially curb the terrorist threat may prove as misguided as the hope that removal of Pablo Escobar, once leader of Colombia’s most powerful and violent drug cartel, would thwart drug trafficking. After the Colombian police killed him, Escobar was quickly replaced by drug lords at least as cunning and violent. Today the drug "war" is in fact fiercer than ever. The "war" on terrorism will be no different. It will be permanent, with elusive and changing enemies and no assurance that major victories will result in the enemies’ ultimate defeat. As good as it may feel to call this conflict a "war," it bears no resemblance to those that have come before it.

Should defeating terrorists be the most important foreign policy priority for the United States in the foreseeable future? After all, before the attacks on the World Trade Center and the Pentagon, the United States was facing numerous foreign policy challenges for which it had no obvious response. It still is.

The renewed focus on terrorism has offered an opportunity to improve U.S. relations with Russia and China, but the Bush administration is still defining its long-term strategy toward those two countries. It is not clear, for example, what stance the Bush administration will take toward China: strategic ally or future threat? Will it ignore Russia or actively engage it? While the NATO alliance has strongly supported the United States, multiple rifts and disagreements — from missile defense to the Kyoto Protocol — still plague relations between Europe and America. Plan Colombia. Tensions between India and Pakistan, China and Taiwan, or the two Koreas. The Balkans. Nuclear proliferation. Africa. AIDS. Poverty. Global financial instability. Argentina and Turkey. The Middle East.

Some of these are chronic problems. Some are dormant and do not require immediate attention. Others will not directly affect major American interests. But sooner or later, one or more of them that does touch vital American interests will flare out of control, and the United States will not have the luxury of not getting involved. Soon, the American public will be forced to change the subject as the national debate shifts from terrorism to rising unemployment and as economists replace security experts on talk shows. These economists, however, will not be discussing the size of the "lock box" but the looming budget deficit and inflation. Indeed, the slow economy is already directly affecting more American lives than did September’s attacks.

The good news is that this tragedy has revived the idea that even the world’s most powerful country cannot afford to go it alone. Perhaps now, many of the unilateralist instincts evident at the beginning of the Bush administration will be tempered by the realization that the long-term fight against terrorism requires close cooperation with other countries. And the lesson that even the most powerful nation depends on the goodwill and cooperation of other governments is likely to carry over when the United States has to deal with its other foreign policy challenges.

But it would be truly tragic if the United States were to renounce one intellectual form of unilateralism only to adopt another. A single-minded war against terrorism may provide an expedient rallying cry for promoting national unity and holding together a patchwork coalition of historical friends, reluctant actors, and opportunistic participants. But in a world whose varied challenges defy simplistic slogans and solutions, making such a "crusade" the lodestar for U.S. foreign policy is a recipe for disaster.