As Washington was fretting about ballistic missiles, 19 hijackers used commercial airliners to kill more Americans than had died in any previous attack in the country's history. And there could be worse to come. The United States is the target of a few hostile nations and well-organized terrorist groups, some of them state-sponsored. They understand that nuclear or biological weapons could do the job even better. To meet these new threats, Washington must pursue three simultaneous strategies: prevention, deterrence, and defense. Missile defense is not the whole answer -- and it could even become part of the problem.
William J. Perry, Professor in the Department of Management Science and Engineering at Stanford University, served as U.S. Secretary of Defense from 1994 to 1997.
THE NATURE OF THE PROBLEM
In the wake of the attacks on the World Trade Center and the Pentagon, America has been mourning its dead and tending to its wounded. But the country also has been building up an angry resolve to respond to this outrage against humanity, and a pragmatic resolve to reduce its vulnerability to future attacks. The world has seen just how terrible the consequences can be when terrorists have the hatred to murder innocent civilians, the resources to coordinate and conduct systematic operations, and the fanaticism to sacrifice their own lives. The evil genius who conceived of using a passenger airplane in kamikaze mode calculated that its 200,000 pounds of jet fuel would make it a weapon of mass destruction. And so it was, with more than 3,000 deaths resulting from each plane used against the World Trade Center, more than ten times the fatality rate caused by past attacks with truck bombs.
The United States can take many actions to make this sort of attack more difficult to carry out, and it will do so, despite the inconvenience and expense. But as Washington moves to reduce the vulnerabilities exposed by the last strike, it should also try to anticipate the next one. As deadly as the World Trade Center disaster was, it could have produced a hundredfold more victims if the terrorists had possessed nuclear or biological weapons. And the future threat could come from hostile nations as well as terrorists.
Nuclear or biological weapons in the hands of terrorists or rogue states constitute the greatest single danger to American security -- indeed, to world security -- and a threat that is becoming increasingly less remote. Several nations hostile to the United States are already engaged in covert programs to develop nuclear weapons, and multinational terrorist groups have demonstrated both by word and by deed that their goal is to kill Americans and destroy symbols of American power. Such terrorists have escalated their methods from truck bombs to the near equivalent of a tactical nuclear weapon, and they clearly have the motivation to go further up the ladder of destruction. Indeed, Osama bin Ladin has told his followers that the acquisition of weapons of mass destruction is a "religious duty." The only question is whether they will succeed.
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The specter of weapons of mass destruction being used against America looms larger today than at any time since the Cuban missile crisis. The World Trade Center bombing scarcely hints at the enormity of the danger. America is prepared only for conventional terrorism, not a nuclear, chemical, or biological weapons catastrophe. With the right approach and organization, however, the United States can be ready. Herewith a plan to reorganize the U.S. government to ensure that it can handle the threats of the next century.
As the recent fiasco with body scanners at airports demonstrated, the United States' homeland security strategy is off track. It has failed to harness two vital assets: civil society and the private sector. Washington should promote a sensible preparedness among individuals, communities, and corporations.
This article appears in the Foreign Affairs eBook, "The U.S. vs. al Qaeda: A History of the War on Terror." Now available for purchase.
The risk of a catastrophic exchange of nuclear missiles has receded. Yet the chances of some use of weapons of mass destruction have risen. Chemical weapons are a lesser threat, but more likely. A vial of anthrax dispersed over Washington could kill as many as three million. Traditional deterrence will not stop a disgruntled group with no identifiable address from striking out at America. The United States must pull back from excessive foreign involvements and begin a program of civil defense to reduce casualties in the event the unthinkable happens.

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