In one sense, America leaves 2001 more powerful than at the start of the year. Within three months, from a standing start, it toppled a government 7,000 miles away in the most inhospitable terrain on earth--the mountains and caves of Afghanistan-- defeating tribes that had beaten back the British and Soviet empires. And it did this largely from the air and suffering almost no casualties. No other country could do this. No other country in the history of the world has done this.

Next year may turn out to be more quiet than we expect. Al Qaeda has been crippled, its base is destroyed and its leaders are on the run. States that have dabbled in terrorism are recognizing that they had better get out of that business. Governments around the world are investigating suspects, closing down bank accounts and tightening up on security procedures. The forces of order seem to be on the rise.

But the forces of disorder have fundamental advantages as well. The ease of communications, transportation and distribution have been crucial to Osama bin Laden's success--and they are only increasing--globalization's advocates often point out that now small, stealthy companies can easily wreak havoc on giant adversaries. Consider September 11 in that light. The total cost of the attack, to Al Qaeda, appears to have been $500,000. The total damage inflicted on the United States economy is estimated to be between $100 billion and $300 billion.

As John Lewis Gaddis of Yale University has pointed out, the stunning payoff and cost-effectiveness of this operation "cannot help but set a standard to which future terrorists will aspire."

We live in an age of disintegration. At the start of this century there were about 60 countries in the world. Now there are 190, most of them small, poor and unstable. Globalization is often spoken of as a force for integration and harmony, but that is true for a few dozen countries with strong, secure governments. For the rest it accelerates the whirlwind of change. Terrorists thrive within the cracks of foundering states, such as Sudan, Somalia, Afghanistan and Pakistan, which is why it has proved difficult even now to find bin Laden and his associates.

"The forces of order and the forces of disorder are set to clash over the next years," says Harvard University's Stephen Walt. And to some extent the outcome of this tussle will depend on the role played by the most powerful country in the world, America.

Even before the Afghanistan campaign, America was well aware of its might. Comprising 4.6 percent of the world's population, it accounts for 21 percent of world economic output. The Pentagon spends more money than the next nine great powers combined. And yet September 11 happened. Indeed, one might argue, that is why it happened. Because America is No. 1, it is also target No. 1. And our enemies attacked in the way they did because they know that only "asymmetrical warfare" offers any hope of success. The most important lesson of September 11 for America should be that in today's world, power alone--even unmatched power--does not produce safety.

Ever since the end of the cold war the United States has sought to use its great wealth and influence to insulate itself from the troubles of the globe. In the months preceding September 11, the Bush administration went several steps farther. All its initiatives and statements--national missile defense, the withdrawal from six treaties in as many months, the criticism of nation-building--were efforts to disentangle itself from the rest of the world. Walt explains, "They wanted to be strong but hover above the rest of the world. Their model was Muhammad Ali. 'Float like a butterfly, sting like a bee'--and then fly away."

But the world comes back to bite you. And now safety lies not in distance or independence, but in engagement. In order to conduct its military operations effectively, the United States had to pursue a rapprochement with Pakistan and Russia, forge new ties with other neighbors of Afghanistan, calm the fears of India and Israel, and garner international--and particularly Islamic--support for its actions. And that was the unilateral part of this campaign!

Now comes the slower, more complex process of rooting out the Qaeda network from dozens of countries, shutting down bank accounts, closing safe houses and arresting suspects. None of this is going nearly as well as the war in Afghanistan did. To make it go better, Washington will have to have sustained international cooperation.

America has tended to view international affairs as an act of charity. We go forth into the world doing good--rebuilding Europe, providing foreign aid, combating communism. (The world is strikingly ungrateful for this beneficence, so eventually we tire of it and go home.) But this time it's about us, not about them. We need the world as much as they need us. International cooperation directly bolsters America's security.

In the years ahead, in the fight against disorder, the United States will have to flex its military muscle often. But it will also learn to better use all the other tools of foreign policy. It will be the ultimate irony, if the legacy of Osama bin Laden's barbarism is to bring the United States into a close, cooperative relationship with the rest of the world.