In response to September 11 the Bush administration crafted a national security strategy whose core mandate is to stop the spread of weapons of mass destruction (WMD) to potential enemies of the United States, using preventive or preemptive military means if necessary. Indeed, the Administration’s public case for initiating war against Iraq was based almost entirely on Iraq’s alleged possession of some WMD, and on the possibility of its gaining more in the future. Since December, as first North Korea and now Iran have declared that they have programs underway that would allow them to produce WMD, a whole series of “WMD wars” seems likely.

Whatever the merits of the case for war against Iraq, the terms of debate about the Bush administration’s larger strategy are flawed. The new emphasis on WMD has not been accompanied by any serious public discussion of the differences among such weapons. A security strategy that fails to acknowledge those differences and their consequences for U.S. foreign and military policies is doomed to failure—in Iraq and elsewhere.

The standard definition of WMD lumps nuclear, biological, and chemical weapons into one category. This classification—which puts three very different weapons into one group—is misleading and dangerous. Nuclear weapons require materials that are extremely difficult to obtain, but once you have the necessary materials the weapons are relatively easy to produce and deliver. Moreover, there is essentially no defense against their explosive effects. In contrast, biological and chemical weapons are produced from “materials” that are widely available. They are also relatively easy to produce and deliver, but it is possible to develop significant defenses against their effects, especially given immediate warning of their use. (In both cases, it is almost impossible to prevent their delivery.) The policy implications are clear: the key to defense against nuclear weapons is to prevent their proliferation, whereas the most effective defense against chemical and biological weapons is to counter the effects of their use.

These two challenges are fundamentally different; it is particularly harmful to gloss over these differences when the possession of WMD is used as a justification for war. Many states have chemical and/or biological weapons, and essentially all states are capable of producing them. Furthermore, the production of chemical and/or biological weapons is relatively simple and can be done on a scale small enough so that even small groups could likely accomplish this task covertly. It is essentially impossible to verify that no chemical or biological weapons are being produced within a state’s borders, or that a state has fully disposed of stockpiles of such weapons.

In contrast, it is very difficult for a state to hide the fact that it is seeking to produce or is producing the materials needed to make nuclear weapons. The technology is beyond the indigenous capabilities of many countries, and aspiring nuclear powers must often obtain it through illicit transfers from other states. Few states with the requisite capabilities are willing to provide such technology because of strong international norms against their export; those that do generally face strong sanctions from the international community. But even assuming success at that stage—as in the recent case of Pakistan providing North Korea with uranium-enrichment technologies—the aspiring nuclear power still faces the multi-year process of constructing an industrial scale facility and operating it long enough to produce an initial stockpile of weapons. Given the scale of the required facilities, and the unique signatures associated with their operation, accomplishing this task covertly is quite unlikely and next to impossible if the international community is paying attention.

Thus, it is possible to sustain a nuclear nonproliferation regime founded on two basic elements: first, international controls can normally prevent states from importing the technology needed to produce nuclear weapon materials; and second, in those rare cases in which these controls fail, the use of diplomacy—and ultimately military force—can be used halt the construction and operation of nuclear-material production plants before they have produced sufficient material for a bomb.

For example, North Korea’s nuclear weapons program is described by many as evidence of the inherent difficulty in halting the spread of nuclear weapons. In fact, it shows only the difficulty of stopping nuclear proliferation solely by controlling the spread of technology for producing nuclear materials. It is true that some determined countries will, over time, succeed in developing the technology largely on their own. In other cases they will find willing assistance from sympathetic allies with the requisite technology. For example, North Korea’s plutonium production program uses a reactor and reprocessing plant that were built in the 1980s with little outside assistance. For its more recently exposed uranium-enrichment program it bartered ballistic missiles for technical and material assistance with gas centrifuges from Pakistan, starting in the late 1990s. But both these efforts also demonstrate the potential vulnerability of all such programs to preventive or preemptive attack. It took years for the North Koreans to build their reactor/reprocessing complex; it will take years for them to build their centrifuge facility. And both efforts were detected well before completion.

Chemical and biological weapons are different. It is impossible to limit the spread of the technology used to make them, and it is impossible to prevent the covert production of such weapons. It is possible, however, to defend against them once they have been delivered. Even simple masks can prevent inhalation of the particles which are the main means of exposure to poison gases or infection by pathogens, and in those rarer cases when exposure or infection can occur through the skin, a protective suit or a visit to a shelter with the proper air filtration system will prevent contact. Military organizations learned long ago how to defend themselves from such weapons, which is one of the main reasons why they largely disappeared from the battlefield after extensive use by both sides in World War I.

The main problem with chemical and biological weapons is the threat they pose to civilian populations, which need immediate warning if an attack has occurred in order to erect or exploit proper civil defenses. Today, however, that warning would most likely result only after the effects of the attack are felt. In other words, we would find out we were under biological attack only after people were already sick or dying from anthrax or smallpox (as happened on a small scale with the anthrax attack after 9/11).

One of the best ways to improve defenses against chemical or biological weapons attack would be the development of a nationwide early-warning system. In essence, such a system would exploit the fact that chemical and biological weapons consist of particles of a certain size, shape, arrangement, and so on and that delivery of such weapons requires that these particles be released into the atmosphere. Once in the atmosphere, there are, in principle, methods available to detect and identify such particles and distinguish them from the normal particulate background. (This is basically how smoke detectors work.) The idea would be to deploy such detectors widely and use them to warn people to adopt the protective measures described above.

To be sure, chemical or biological weapons present very serious dangers to civilian populations. But with intense effort, sponsored by the new Homeland Security Agency, we could develop reasonably effective civil defenses against chemical or biological attack.

The public case for war against Iraq is based overwhelmingly on the need to destroy what WMD it has and to prevent the further development of more. But even with a massive invasion of the country and the installation of a new regime, the United States will be no more capable of ensuring that Iraq lacks chemical or biological weapons than it has been of finding within its own borders the perpetrator of the post–9/11 anthrax attacks and the source of the spores. By contrast, North Korea and now Iran have demonstrated that the international community is likely to detect the indigenous development of nuclear weapons years in advance of their completion. Of the three members of the “axis of evil,” Iraq has the least advanced nuclear program, assuming it has one at all. In fact, it is so far behind the other two members of the “axis” that it is not yet possible to use military force against Iraq’s program because it has not yet begun to construct what would be the main military target, the nuclear material production facilities.

The fact that Iraq is at best at the very earliest stages of nuclear development has not been widely discussed in the debate over its alleged WMD capabilities, but it was explicitly acknowledged in the report on Iraqi WMD issued by the British intelligence community. The Bush administration, perhaps acknowledging this reality, has often suggested another means for Iraq to quickly acquire nuclear weapons—by directly purchasing or stealing nuclear materials or entire weapons from within the vast, ill-guarded post-Soviet nuclear complex in Russia. Certainly, if it were possible to make such purchases in Russia or elsewhere, the nuclear nonproliferation regime would collapse. But it is also certain that the best way to avoid such a scenario would be to engage Russia directly with more-aggressive programs to secure those weapons and nuclear materials, rather than invade, occupy, and change the regime of every potentially hostile nuclear aspirant in the world. Ironically, the Bush administration’s initial approach to the problem of insecure nuclear materials in Russia was to reduce funding for programs designed to improve the security of Russia’s nuclear complex. There has been no major initiative since 9/11 to reverse this neglect.

The most important ways to prevent nuclear-weapons development are primarily diplomatic, including the traditional nuclear nonproliferation regime, which restricts traffic in the means of producing nuclear materials, as well as the more recent challenge of improving, in cooperation with Russia, the security of excess stockpiles of weapons and materials. But a significant nuclear nonproliferation role may remain for military force, or for coercive diplomacy backed by the explicit threat of force. Any state that wishes to develop the capability to produce nuclear weapons must endure a window of vulnerability measured in years, during which its intentions will be clear but its capabilities will not yet have reached fruition. During that period the threat of military preemption will be an important tool of the United States, and of the international nuclear nonproliferation regime that it supports, preferably to spur a diplomatic solution but also to be a last resort for forcibly preventing further proliferation.

Given these realities a strategy that focuses on military solutions to the spread of WMD has obvious dangers. Such a strategy logically would lead to many wars with many countries, because essentially all countries have or are capable of easily producing chemical or biological weapons. These wars will not be limited, because the goal of eliminating chemical or biological weapons demands invasion and regime change. Yet, because such weapons cannot be found and destroyed from a distance, such wars will still leave some weapons available to an opponent and eliminate whatever incentives that opponent might have to withhold them.

As for preventing nuclear proliferation, a highly militarized approach emphasizes only the least usable of the tools available. Even with a window of vulnerability during the period of nuclear development the military option will not always be credible, for a variety of political reasons. The Bush administration is demonstrating this by its different responses to Iraq’s and North Korea’s nuclear programs.

Finally, a too-militarized approach to preventing WMD attacks threatens distraction from more constructive policies. First, the existing nuclear nonproliferation regime that focuses on preventing the spread of the means of producing nuclear materials is not perfect, but we have no alternative to it. Policy failures, when they occur, must be greeted by efforts to strengthen the regime rather than abandon it. Second, alongside the challenge of shoring up this regime is the more recent challenge to better secure nuclear weapons and materials in Russia. Here again, the cost of failure would be enormous, and success depends on giving priority to the diplomatic efforts needed to get Russia to meet more-aggressive standards of weapon and material security (rather than, say, the diplomatic efforts to pave the way for national missile defenses). And third, the potential ability to defend against the effects of chemical and biological weapons will remain just that if too much effort is devoted to the chimera of treating them like nuclear weapons, whose development and spread can be prevented or limited at the source. The civil defenses needed to protect civilian populations from chemical or biological weapons attack will likely only be developed and deployed if the lack of any truly viable alternatives for dealing with this threat is acknowledged.