The United States, for the foreseeable future, will continue to have the capability to help shape the global environment, working together with allies and like-minded states to contain and sometimes reduce conflicts, says Nye. But he notes that the United States faces "a new form of threat" -- from terrorists using weapons of mass destruction or launching attacks on critical infrastructures -- for which "our traditional security instruments are ill suited." Before assuming his present post as dean of the John F. Kennedy School of Government at Harvard University, Nye served as assistant secretary of defense for international security affairs in 1994 and 1995; chairman of the National Intelligence Council, which coordinates intelligence estimates for the president, in 1993 and 1994; and, from 1977-79, as deputy to the under secretary of state for security assistance, science and technology.

The world has seen important changes in the distribution of power over the past decade. The Soviet Union has collapsed and Russian power remains in decline. China's influence, on the other hand, has risen rapidly and is likely to continue to grow. Yet despite these dramatic developments, the central reality of the global balance of power is the same as it was in l990: the United States remains the only superpower with global assets in all dimensions of power -- military, economic, and political. Those who forecast an inevitable American decline only a decade ago have been proven wrong as the world enters a new century.

This does not mean that a unipolar world has replaced the bipolar balance of the Cold War. There are many important security, economic, and political goals that the United States cannot achieve by itself. Nor is it accurate to call the world multipolar so long as every state except the United States lacks one or more key power resources. Instead, power is distributed in a complex pattern something like a three-dimensional chess board. On the top board, military power is largely unipolar, with the United States as the only country with both intercontinental nuclear weapons and large, modern air, naval, and ground forces capable of deploying around the globe. On the middle board, economic power is tripolar, with the United States, Europe, and Japan representing nearly two-thirds of world product. China's growth will make economic power quadripolar after the turn of the century. On the bottom chess board, the transnational relations that cross borders outside the control of government include actors as diverse as bankers and terrorists. Here power is widely dispersed.

Just as important as these changes in the distribution of power are three changes in the nature of power and the processes through which it can be exercised. First, economic instruments of international power have been growing in importance for several decades. This should not be overstated, however, as some have done by suggesting that economic power has replaced military power as the central medium of world politics. Economic instruments still cannot compare with military forces in their coercive and deterrent effects. Economic sanctions alone were not sufficient to persuade Iraq to withdraw from Kuwait. Moreover, a single regional security crisis can cause stock markets to crash and stifle investments. Instead, economic and political security are closely intertwined, as was seen in the recent Asian financial crisis.

Second, modern weapons have changed the role of military power. There are two contradictory trends. On the one hand, the great powers' acquisition of nuclear weapons has for several decades made the possibility of direct conflict between them seem unthinkably costly. Thus such weapons have become musclebound, and useful only for deterring others. On the other hand, changes in information technology (including computers, sensors, and satellites) have made possible a new generation of smart weapons that allow great precision and minimal collateral damage. These trends make military power less costly and more usable.

The third and perhaps greatest change in the nature of power has been the increasing importance of soft power, which is due in large part to the information revolution that is transforming the world. Soft power is the ability to achieve desired outcomes in international affairs through attraction rather than coercion. Hard power, including the coercive use of military force or economic sanctions, seeks to get others to do what we want. Soft power aims to get others to want what we do. Such soft power can rest on the appeal of one's ideas or the ability to set the agenda in ways that shape the preferences of others. The United States remains a global leader in soft power resources, as is evident in the movement toward democracy and free markets in more than 30 states over the past decade.

Yet the paradox of American security and foreign policy in the 2lst century remains: even as the most powerful state, the United States cannot achieve all its international goals by acting alone. The country lacks both the international and domestic prerequisites to resolve every conflict. In each case, its role must be proportionate to the American interests at stake and the costs of pursuing them. Thus the United States must continue to enable and mobilize international coalitions to address shared security threats. The Gulf War and the peacekeeping force in Bosnia are cases in point.

The end of the Cold War reduced but did not eliminate the possibility of world wars among great powers. Regional and local wars are more likely than global conflicts. Nonetheless, security among states is greater because territorially defined resources have declined in importance among the great powers. In the past, leading states were tempted to acquire land for its raw materials, agricultural potential, industrial factories, or strategic importance as either a platform for military attacks or a buffer against attacks by others. These motives for forcible acquisition of territory are much less powerful today. Modern economic production depends as much on human capital and services as on territory. Perhaps most important, great power conflict has become less likely because many of the great powers are either already democratic or aspiring to become so, and history shows that liberal democracies are less likely to fight one another. For this reason the advancement of democratic processes in Russia and of pluralization and human rights in China are security, as well as moral, objectives of American policy.

Regarding regional and local conflicts, American power can be an important factor in limiting their frequency and destructiveness. In some cases, it is even possible to reduce the level of conflict in civil and domestic disputes. While the United States cannot be a lone global policeman -- the American public does not want such a role -- it can at times serve as "sheriff of the posse" that leads shifting coalitions of friends and allies to address shared security concerns. This requires sustained attention to the institutions and alliances that add leverage to American power. It also requires investment in military forces and attention to their global deployment.

The American military budget has been cut by 40 percent and the armed forces personnel by a third since the Cold War peak. Nonetheless, we still station about 100,000 troops in Europe, another 100,000 in Asia, and 20,000 in and around the Persian Gulf. Combined with the prepositioning of equipment and joint exercises with allies and friendly countries, these capabilities help to shape the political environment in those critical regions and thus act as a form of preventive defense. These forces are welcomed by major countries in these regions. NATO has not lost its popularity in Europe and is adapting its mission to a post-Cold War world. In Asia, many leaders fear that an American withdrawal would lead to an arms race in the region and the loss of the political stability that has provided a foundation for the region's remarkable economic growth. When the Defense Department issued its East Asian Strategy Report in l995, promising to keep up its alliances and forward deployments, the report was widely welcomed.

A critical security threat in the post-Cold War world is the spread of weapons of mass destruction. Thus far the nuclear non-proliferation record is impressive. In l963, President John F. Kennedy predicted that there would be dozens of nuclear states by now. Certainly there are that many states capable of developing such weapons. But most have chosen to forego the bomb. There are the five nuclear weapons states enumerated in the l970 Non-Proliferation Treaty (the United States, Russia, Britain, France, China); India and Pakistan, which recently carried out nuclear tests; and, by reputation, Israel. South Africa, which had developed a half dozen bombs in the l980s, subsequently gave them up. And rogue states such as Iraq and North Korea have had their programs halted. The permanent extension of the NPT in l995 was an encouraging sign that the non-proliferation regime was holding.

The greatest threat in the nuclear area now is the problem of so-called "loose nukes," the danger that bombs or nuclear materials might escape from control in states of the former Soviet Union and become available on the black market. American assistance to Russia in this area, through the Defense Department's Cooperative Threat Reduction Program, is a new and different type of security policy for a new world. Non-proliferation policy in all its dimensions, including the spread of chemical and biological weapons and their means of delivery, remains at the heart of our security policy.

Finally, there is a new dimension of security problem that cannot be solved by classical military means. That is the threat of terrorists using weapons of mass destruction. For 40 years, Americans lived under the fear of Soviet nuclear attack. The end of the Cold War reduced the prospect of a nuclear holocaust, but ironically, prospects of a nuclear explosion inside the United States have probably increased. And the threat is not exclusively nuclear. Terrorist access to biological and chemical weapons such as anthrax, ricin, or sarin is easier than access to nuclear materials.

Recent years have seen the rise of a new type of terrorist less interested in promoting a political cause and more focused on the eradication of what they define as evil. Their motives are often a distorted form of religion, and they consider weapons of mass destruction to be a suitable means to their ends. Such devices are becoming more available. The rise of mafias in former Soviet states has brought an increase in the smuggling of nuclear materials (mercifully in small amounts thus far). Chemical and biological agents can be produced by graduate students or lab technicians. General recipes are available on the Internet. In l995, a Japanese sect used sarin in the Tokyo subway, killing l2 people. They also experimented with biological agents. Recently President Clinton signed presidential directives designating terrorism and threats to critical infrastructures (including information systems) as top priorities for American security policy.

In conclusion, the world after the Cold War has good and bad news for American security policy. At the military and economic levels, the United States is likely to remain the preponderant power for the foreseeable future. No other state can match American strength. The prospect of great power war is unlikely. The United States has the capability to help shape the environment so as to reduce the prospects of future threats. While this does not mean that the United States can (or wishes to) act as a world policeman or would be able to control all conflicts, it does mean that when it chooses to organize coalitions with allies and like-minded states, there are reasonable prospects for containing and sometimes reducing conflicts. On the other hand, the bad news is that at the transnational level, where there is great dispersion of power and no one is in control, a new form of threat has arisen for which our traditional security instruments are ill suited. This is an area that will require more attention in the future.