Throughout the cold war, the Soviet Union posed a threat to the very survival of the United States. But with the cold war over, it is necessary to rethink the risks to U.S. security. Conceptually, they can be arrayed in a hierarchy from most dangerous to least dangerous. At the top of the hierarchy would be an "A list" of threats to U.S. survival of the kind and scale that the Soviet Union presented during the cold war. But this list is empty today: there are no imminent military threats to the very survival of the United States. The two "major regional contingencies" in the Persian Gulf and on the Korean peninsula that undergird Pentagon planning and budgeting form a "B list" of imminent threats to U.S. interests, but not to the survival or way of life of Americans. The third place in this hierarchy is occupied by the Kosovos, Bosnias, Somalias, Rwandas, and Haitis that compose a "C list" of important contingencies that indirectly affect U.S. security but do not directly threaten U.S. interests.

The emptiness of the A list is disorienting for Americans, who made the huge transition from defeating aggression to deterring aggression after World War II, but who now, in consequence, tend to conceive national security strategy exclusively in terms of threats to be deterred or defeated. Thus the focus tends to be on B-list and C-list threats. We believe, however, that long-range strategic thinking about how to prevent the rise of new A-list threats is sorely needed, and it is for that reason we have written this book.

Political and economic transformations now under way in Eastern Europe and the former Soviet Union are unprecedented in their scale and scope. This vast redistribution of political and economic power extends throughout Eurasia, and includes the gradual emergence of China as a true world power. Meanwhile, the nuclear, chemical, and biological weapons that made deterrence both dangerous and necessary have not been fully dismantled, let alone disinvented, and they now threaten to fall into the hands of unstable nations, groups, and terrorists. Thus while threats of the traditional sort might be hard to find, danger to the security of Americans is not.

However, in the years since the cold war ended, the evening news has given the impression that the primary security challenges of the new era are those that arise in remote places such as Kosovo, Bosnia, Rwanda, Haiti, and Somalia. For many, these conflicts seem to define the national security dangers of the post-cold war world. But in fact, these are third-order or C-list threats; they are places and problems that do not threaten America's survival as World War II and the cold war did. This is not to say that they are unimportant; we must meet challenges such as Bosnia not only for humanitarian reasons, but to stop the killing and atrocities before they undermine the foundations of regional and international stability. However, a price is paid for such actions: resources are diverted to military operations, and they demand the time and attention of our national leaders. Because such C-list issues do not threaten America's vital security interests, dealing with them individually or as classes--peacekeeping, peacemaking, humanitarian operations, operations other than war, and the like--cannot make up the core national security strategy of the United States.

Nor can U.S. strategy be wholly determined by what we call B-list threats: those that may threaten vital U.S. interests, but not America's survival. These are the major regional contingencies -- specifically , the threat of Iraqi aggression in the Persian Gulf and the threat of North Korean invasion of South Korea -- around which the Pentagon must organize much of its military planning and force structure. While a look at the newspapers suggests that the United States places a high priority on peacekeeping and humanitarian operations, a look at the defense budget shows the higher priority the United States places on these regional wars. They constitute familiar cold war-like strategic territory for Americans: clear and imminent threats, which must be deterred by ready military forces.

If deterrence fails, the U.S. military is capable of inflicting a decisive defeat on today's two potential regional aggressors. Saddam Hussein's Iraq is militarily weaker today than it was in 1990, while U.S. forces are better positioned to repel Iraqi aggression. North Korea still has the capability to launch a horribly destructive war on the Korean peninsula, but the capability of its collapsing economy and starving population to sustain the campaign is far less than during the 1994 crisis over North Korea's nuclear program. And, as in the Gulf, the posture of the United States and the U.S.-Korean Combined Forces Command has been substantially improved.

The reason for the preoccupation of American strategy with these B-list and C-list issues in the early post-cold war period has been the current unusual and happy circumstance in which there is no A-list threat to the United States. The Soviet Union is gone. Russia does not pose a conventional military threat to Europe and shows little inclination to pose a nuclear threat to the United States. Some Americans conjure up China as the enemy of the future, but China's future role in the world will be influenced by contingencies over which U.S. policy can exert some positive influence.

Thus, the United States is enjoying a period of peace and influence like it has never had before. But while this should be savored by the public, foreign policy and defense leaders cannot afford to be so complacent. A period of absence of A-list threats must stretch us strategically; it calls for vision and foresight to act strategically when events and imminent threats do not compel us to do so. That should be the primary business of statecraft in the post-cold war era.

The way to sharpen focus on the strategic requirements of our time is to ask the questions, "How might the post-cold war era end?" "How can the United Stares prolong this period of peace and influence?" "How can we ensure that if it must end, it ends gracefully, without cataclysm?" and "What is the character of the era that will follow it?" The answers to these questions define the fundamental long-term strategic challenges of the post-cold war era.

Because the security strategy created to deal with the threats of the cold war is not suitable for dealing with the dangers to our security in the twenty-first century, we believe that the United States should now follow the example of Truman, Marshall, and Acheson at America's last great strategic transition: it should formulate a new security strategy appropriate for this new world and should create the policies and programs capable of carrying out that strategy. In essence, America has another chance to realize Marshall's initial vision at the end of World War II: a world not of threats to be deterred, but a world "united in peace, freedom, and prosperity." To realize this vision, America should return to a prevention strategy like that embodied so successfully in the Marshall Plan: a strategy of Preventive Defense.

Preventive Defense is a defense strategy for the United States in the twenty-first century that concentrates national security strategy on the dangers that, if mismanaged, have the potential to grow into true A-list-scale threats to U.S. survival in the next century, bringing the current era to an abrupt and painful end. These dangers are not yet threats to be defeated or deterred; they are dangers that can be prevented.

We argue that developing and implementing a strategy of Preventive Defense is the most important mission of today's national security leaders and defense establishment. They must dedicate themselves to Preventive Defense at the same time they deter lesser but existing threats--in Iraq and North Korea--and conduct selected peacekeeping and humanitarian missions--in Bosnia, Haiti, Rwanda, and so on--where conflict threatens long term interests.

In the first five chapters of this book, we focus on the five dangers that we believe have the potential to become A-list threats to U.S. and international security in the twenty-first century. These are the targets of Preventive Defense; its goals are to keep these dangers from becoming major threats. We define these dangers as follows:

--that Russia might descend into chaos, isolation, and aggression as Germany did after World War I;

--that Russia and the other Soviet successor states might lose control of the nuclear legacy of the former Soviet Union;

--that China could grow hostile rather than becoming cooperatively engaged in the international system;

--that weapons of mass destruction will proliferate and present a direct military threat to the United States;

--that "catastrophic terrorism" of unprecedented scope and intensity might occur on U.S. territory.

We devote a chapter to each of these dangers, beginning each with an illustrative tale drawn from our time in office and then offering an analysis of the issues and a set of Preventive Defense prescriptions for U.S. policy.

However, Preventive Defense could fail and any of these dangers become A-list threats. Therefore the United States will continue to need a strong military on into the twenty-first century, and so chapter 6 addresses the management issues of keeping it so.

Harking back to the disastrous failures of the international community in dealing with Germany after World War I, we focus attention on the risk of parallel developments in post-Soviet Russia. A primary goal of Preventive Defense is to help Russia establish a self-respecting place for itself in the post-cold war world and to establish a stable security order on the territory of the former Warsaw Treaty Organization states. In chapter 1 we tell the story of how we sought to forward these ends by "defense diplomacy," engaging Russia in mutually beneficial cooperative efforts and particularly in the NATO-led international peacekeeping force sent to Bosnia to enforce the Dayton Accords. Such defense diplomacy grows even more important as the "honeymoon" phase of the post-cold war "partnership" with Russia ends, the Yeltsin era draws to a close, and a more difficult era begins.

Failure to reduce and secure the deadly legacy of the cold war -- nuclear, chemical, and biological weapons in Russia and the rest of the former Soviet Union -- could quickly resurrect a top priority A-list threat if these weapons were to fall into the hands of disaffected custodial personnel, rebellious actions, rogue regimes, or terrorists. In chapter 2, we relate the history and successes of the Nunn-Lugar Cooperative Threat Reduction program and other efforts to control the lethal legacy of the cold war. But our success so far is only small comfort in view of the sheer size of that legacy and its longevity: plutonium, for example, has a half- life of twenty four thousand years, an eternity in Russian politics. As Russia enters the second post-cold war era, arms control has been at an impasse, and threat reduction programs such as Nunn-Lugar need reinvention and reinvigoration.

Chapter 3 argues that the United States must act to help shape the course of China's rise to Asian superpower status so that it emerges in future decades as a partner rather than an adversary. Failure here would lead to the Pacific's greatest danger. We give a glimpse of that danger by describing the 1996 crisis over China's missile firings into the waters around Taiwan. The Clinton administration has called for a strategy of "engagement" in the U.S.-China relationship that reflects the principles of Preventive Defense, but engagement needs specific content if it is to be more than just a diplomatic slogan. Chapter 3, therefore, outlines content for U.S. engagement with China based on Preventive Defense principles.

The spread of weapons of mass destruction (WMD) has always been regarded as a cardinal danger to international peace and security, but the nature of proliferation is now sharpening from diplomatic problem to direct military threat to the United States and its interests. Potential opponents in regional conflicts are amassing weapons of mass destruction in an attempt to sidestep U.S. conventional military forces, which they cannot hope to defeat in head-to-head "symmetric" warfare. The U.S. military therefore needs to develop counters to "asymmetrical" threats like weapons of mass destruction. In chapter 4, we describe the way the proliferation danger nearly became a direct threat on the Korean peninsula in 1994 and our efforts to promote military countermeasures in the so-called Counterproliferation Initiative. But this effort to equip the U.S. military for asymmetrical warfare is only beginning; chapter 4 charts the next steps.

The widening availability of destructive technology and the growing complexity and consequent vulnerability of twenty-first century societies suggest that terrorism might make a quantum leap in the decades ahead, from airline hijacking, ordinary explosives, and hostage taking to attack with nuclear, chemical, biological, and cyber weapons of enormous destructiveness. Terrorism with such weapons could cross borders as easily as people, goods, and capital do, bringing the threat directly to the U.S. homeland for the first time. To many, the end of the cold war implied that threats to U.S. personnel and interests would be remote, taking place in Europe, the Persian Gulf, or the Korean Peninsula. However, this threat has the potential to change Americans' perception of their security within their own homeland and thus to change our society itself; we therefore term this specter "catastrophic terrorism." It is a military-scale threat divorced from the traditional context of foreign military conflict, and this is entirely new in American experience. Catastrophic terrorism challenges the U.S. government to invent a new security structure from the bottom up. Chapter 5 reports the results of an effort, with our colleagues John M. Deutch and Philip Zelikow, to lay the first bricks in that structure.

We have argued that the end of the cold war has induced a false sense of comfort that the dangers to American security are confined to the B-list and C-list threats that have dominated the headlines in the last decade of the twentieth century. There is growing evidence that the absence of imminent A-list threat might also lull the United States into sloppy and wasteful mismanagement of its defense establishment. We call the danger of such mismanagement "the threat within." Chapter 6 describes this threat and the actions already taken to overcome some of its consequences. However, we argue, a new effort is needed. The United States must have a strong military to cope with continuing B-list and C-list contingencies, and a strong military will be even more essential if Preventive Defense strategies are not able to keep future threats from emerging.