What took place on Tuesday was not a crime; it was war. The scale of the attacks, their coordination, and their sinister calculation of timing and place bespeak organizations that have honed their skills over many years. To deal with them and with those who harbor or protect them, the United States must understand that they are not criminals; they are enemies. There should be no talk of "tracking down the perpetrators" or "bringing the guilty to justice." This is not about cops and robbers, nor about international courts. It is, rather, war--hideous, brutal, and merciless war.

What does it mean, under these circumstances, to wage war? It begins with a willingness to attack those responsible with every intention of killing rather than capturing them. Although the United States has from time to time dropped bombs or fired cruise missiles with lethal intent, it has thus far flinched at outright assassination ("extrajudicial killings," as the term of art now has it). There were a number of reasons, some significant, for such a policy. But it must end. The issue is not merely retribution but sound strategy, which is why the Israelis have pursued just such an approach in dealing with their terror problem. Terrorist organizations are small and specialized--professional in a twisted sense of the term. Kill or disable a key member of one, and you can disrupt a complex operation. Moreover, when terrorists fear death themselves, more of their efforts are directed toward survival and less toward the planning and preparation of attacks.

Terror, moreover, requires some kind of cover from states--either outright protection and sponsorship or indifference. In recent years the United States has been reluctant to spotlight nations that sponsor terrorism. And even when it does, as in the cases of Iran or Iraq, its response is generally limited to economic boycotts and the like. To understand that this is war is to understand that such states are nothing less than allies of our enemies, and they too should feel the full weight of American hostility. A variety of measures, from cyberattacks to blockades and even bombing, should make the leaders of such countries understand that the penalties for supporting terrorists have increased by an order of magnitude. Neutrals or even American allies who turn a blind eye to terrorist activity should know that they will also pay a heavy, if nonviolent, price.

Domestically, too, much must change. Expenditures on defense will surely grow by tens of billions of dollars, as they should. Much of that money should go to the kinds of forces and systems that can acquire information about terrorists and attack them and their sponsors--sophisticated intelligence-gathering, long-range bombers, cruise missiles and the platforms that launch them, Special Operations forces. Defensive measures will be expensive--command bunkers, ubiquitous metal-detectors and x-ray machines, and other protective devices of all kinds. We will pay a price in convenience and even, perhaps, in the full scope of our personal liberties. We will spend more time waiting in line at airports, find access to government offices more difficult, and quite likely submit to more intrusive monitoring by police and counterintelligence than we have known since the early years of the cold war. We may come to understand, at least in our big cities, the experience of Israelis today or of Londoners several years ago, when IRA bombs meant not being able to go into a cinema without having one's belongings carefully searched. Welcome to the world of omnipresent video cameras, retinal scanners, and perhaps even national identity cards.

This is our generation's Pearl Harbor. In all likelihood, the price in human life will prove even greater and the psychological shock greater still--an attack on our capital and on our foremost city. The task of mobilizing American power, in all its manifestations, now falls on the president and on the government. Not least of the many tasks that rest on their shoulders will be to speak clearly and compellingly to us, to our friends, and to our enemies. To Americans, our political leaders must communicate calm purpose and confident resolve as they mobilize our energies and pass the legislation that will be necessary to take the country to war. To our friends, they must make clear our determination to use whatever means are necessary--including, inevitably, those that are inconvenient or ugly. And to our enemies, they must spell out the consequences they will face. This may mean speaking blunt truths about, for example, the nature of radical Islam, uttering real and precise threats about what we will do to countries that stand in the way of our efforts to crush our enemies, and explaining, after the inevitable collateral damage occurs and we accidentally kill some innocent civilians, that this is an inevitable consequence of war.

If this all sounds grim, it is because this is what war is. But, as we recover from the initial shock and grieving, as we bury our dead and tend to our wounded, busy teams of experts will mine the databases of the airlines and signal-intelligence agencies, and sift through the evidence that undoubtedly exists in the wreckage of the twin towers of the World Trade Center and the smoking hulk of the Pentagon. They will figure out who did this. And when the United States mobilizes, as Tojo and Hitler found out, the results are overwhelming. Sixty years ago, almost to the day, Winston Churchill pondered the news of Pearl Harbor:

Silly people--and there were many, not only in enemy countries--might discount the force of the United States. Some said they were soft, others that they would never be united. They would fool around at a distance. They would never come to grips. They would never stand blood-letting. Their democracy and system of recurrent elections would paralyze their war effort. They would be just a vague blur on the horizon to friend or foe. Now we should see the weakness of this numerous but remote, wealthy and talkative people. But I had studied the American Civil War, fought out to the last desperate inch. American blood flowed in my veins. I thought of a remark which Edward Grey had made to me more than thirty years before--that the United States is like "a gigantic boiler. Once the fire is lighted under it there is no limit to the power it can generate."

The fire has been lit.

Eliot A. Cohen is professor of strategic studies at the Paul H. Nitze School of Advanced International Studies at Johns Hopkins University.

This article originally ran in the September 24, 2001 issue of the magazine.