More than 200 years ago, the philosopher Immanuel Kant defined the ultimate choice before mankind: if world history was to culminate in universal peace, would it be through moral insight, or through catastrophe of a magnitude that allowed no other outcome? We are approaching a point where that choice may be imposed on us. The basic dilemma of the nuclear age has been with us since Hiroshima: how to bring the destructiveness of modern weapons into some moral or political relationship with the objectives that are being pursued. Any use of nuclear weapons is certain to involve a level of casualties and devastation out of proportion to foreseeable foreign-policy objectives. Efforts to develop a more nuanced application have never succeeded, from the doctrine of a geographically limited nuclear war in the 1950s and 1960s to the “mutual assured destruction” theory of general nuclear war in the 1970s.

In office I recoiled before the options produced by the prevalent nuclear strategies, which raised the issue of the moral right to inflict a disaster of such magnitude on society and the world. Moreover, these prospects were generated by weapons for which there could not be any operational experience, so that calculations and limitations were largely theoretical. But I was also persuaded that if the U.S. government adopted such restraints, it would be turning over the world’s security to the most ruthless and perhaps genocidal.

In the two-power world of the Cold War, the adversaries managed to avoid this dilemma. The nuclear arsenals on both sides grew in number and sophistication. Except for the Cuban missile crisis, when a Soviet combat division was initially authorized to use its nuclear weapons to defend itself, neither side approached their use, either against each other or in wars against non-nuclear third countries. They put in place step by step a series of safeguards to prevent accidents, misjudgments and unauthorized launches.

But the end of the Cold War produced a paradoxical result. The threat of nuclear war between the superpowers has essentially disappeared. But the spread of technology — especially the technology to produce peaceful nuclear energy — has vastly increased the feasibility of acquiring a nuclear-weapons capability. The sharpening of ideological dividing lines and the persistence of unresolved regional conflicts have magnified the incentives to acquire nuclear weapons, especially by rogue states or non-state actors. The calculations of mutual insecurity that produced restraint during the Cold War do not apply with anything like the same degree to the new entrants in the nuclear field, and even less so to the non-state actors. Proliferation of nuclear weapons has become an overarching strategic problem for the contemporary world.

Any further spread of nuclear weapons multiplies the possibilities of nuclear confrontation; it magnifies the danger of diversion, deliberate or unauthorized. And if the development of weapons of mass destruction spreads into Iran and continues in North Korea — in the face of all ongoing negotiations — the incentives for other countries to follow the same path could become overwhelming. How will publics react if they suffer or even observe casualties in the tens of thousands from a nuclear attack? Will they not ask two questions: What could we have done to prevent this? What shall we do now so that it can never happen again?

Considerations such as these induced former senator Sam Nunn, former secretary of defense William Perry, former secretary of state George Shultz and I — two Democrats and two Republicans — to publish recommendations for systematically reducing and eventually eliminating the danger from nuclear weapons. We have a record of strong commitment to national defense and security. We continue to affirm the importance of adequate deterrent forces, and we do not want our recommendations to diminish essentials for the defense of free peoples while a process of adaptation to new realities is going on. At the same time, we reaffirm the objective of a world without nuclear weapons that has been proclaimed by every American president since Eisenhower.

Such a world will prove remote unless the emerging nuclear-weapons program in Iran and the existing one in North Korea are overcome. Both involve the near certainty of further proliferation and of further incorporation of nuclear weapons into the strategies of nuclear-weapons states. In the case of Iran, the permanent members of the Security Council have called for an end to the enrichment of materials produced by the program for peaceful uses of atomic energy. In the case of North Korea, China, Russia, Japan, South Korea and the United States have demanded the elimination of its nuclear weapons. North Korea has agreed to abandon its nuclear-weapons program but, by procrastinating in doing so, threatens to create a legitimacy for the stockpile of weapons it has already produced.

I have long advocated negotiations with Iran on a broad front, including the geopolitical aspect. Too many treat this as a kind of psychological enterprise. In fact, it will be tested by concrete answers to four specific questions: (a) How close is Iran to a nuclear- weapons capability? (b) At what pace is its development program moving? (c) What balance of rewards and penalties will move Iran to abandon the program? (d) What do we do if, despite our best efforts, diplomacy fails?

A critical issue in nonproliferation strategy will be whether the international community can place the fuel cycle for the peaceful uses of nuclear energy under international control. Is the International Atomic Energy Agency (IAEA) capable of designing a system that places the enrichment and reprocessing of uranium and plutonium under international control and in locations that do not threaten nuclear proliferation?

Arresting and then reversing the proliferation of nuclear weapons places a special responsibility on the established nuclear powers. They share no more urgent common interest than preventing the emergence of more nuclear-armed states. The persistence of unresolved regional conflicts makes nuclear weapons a powerful lure in many parts of the world — to intimidate neighbors and to serve as a deterrent to the great powers who might otherwise intervene in a regional conflict. Established nuclear powers should strive to make a nuclear capability less enticing by devoting their diplomacy to diffusing these unresolved conflicts.

A new nuclear agenda requires coordinated efforts on several levels: first, the declaratory policy of the United States; second, the U.S.–Russian relationship; third, joint efforts with allies as well as other nonnuclear states relying on American deterrence; fourth, securing nuclear weapons and materials on a global basis; and, finally, reducing the role of nuclear weapons in the doctrines and operational planning of nuclear-weapons states.

The Obama administration has already signaled that a global nuclear agenda will be a high priority in preparation for the Review Conference on the Nuclear Nonproliferation Treaty scheduled for the spring of 2010. A number of measures can be taken unilaterally or bilaterally with Russia to reduce the pre-emptive risk of certain alert measures and the deployment of tactical nuclear weapons.

For more than 30 years after the formation of the Western alliance, the Soviet threat was the motivating and unifying force in Western nuclear policy. Now that the Soviet Union has broken up, it is important to warn against the danger of basing policy on a self-fulfilling prophecy. Russia and the United States between them control about 90 percent of the world’s nuclear weapons. They have it in their control to reduce the reliance on nuclear weapons in their bilateral relationship. They have already done so for 15 years on such issues as the Cooperative Threat Reduction Program. The immediate need is to start negotiations to extend the START I agreement, the sole document for the verification and monitoring of established ceilings on strategic weapons, which expires at the end of 2009. That should be the occasion to explore significant reductions from the 1,700 to 2,000 permitted under the Moscow Treaty of 2002. A general review of the strategic relationship should examine ways to enhance security at nuclear facilities in Russia and the United States.

A key issue has been missile defense — especially with respect to defenses deployed against threats from proliferating countries. The dialogue on this subject should be resumed at the point at which it was left by President George W. Bush and President Vladimir Putin in April 2008. The Russian proposal for a joint missile defense toward the Middle East, including radar sites in southern Russia, has always seemed to me a creative political and strategic answer to a common problem.

The effort to develop a new nuclear agenda must involve our allies from its inception. U.S. and NATO policy are integrally linked. Key European allies are negotiating with Iran on the nuclear issue. America deploys tactical nuclear weapons in several NATO countries, and NATO’s declaratory policy mirrors that of the United States. Britain and France — key NATO allies — have their own nuclear deterrent. A common adaptation to the emerging realities is needed, especially with respect to tactical nuclear weapons. Parallel discussions are needed with Japan, South Korea and Australia. Parallel consultations are imperative with China, India and Pakistan. It must be understood that the incentives for nuclear weapons on the Subcontinent are more regional than those of the established nuclear powers and their threshold for using them considerably lower.

The complexity of these issues explains why my colleagues and I have chosen an incremental, step-by-step approach. We are not able to describe the characteristics of the final goal: how to determine the size of all stockpiles, how to eliminate them or to verify the result. Affirming the desirability of the goal of a world free of nuclear weapons, we have concentrated on the steps that are achievable and verifiable. My colleague Sam Nunn has described the effort as akin to climbing a mountain shrouded in clouds. We cannot describe its top nor be certain that there may not be unforeseen and perhaps insurmountable obstacles on the way. But we are prepared to undertake the journey in the belief that the summit will never come into view unless we begin the ascent and deal with the proliferation issues immediately before us, including the Iranian and North Korean nuclear programs.

A closing word: A subject at first largely dominated by military experts has attracted the commitment of disarmament advocates. The dialogue between them has not always been as fruitful as it should be. Strategists are suspicious of negotiated attempts to limit the scope of weapons. Disarmament advocates occasionally seek to pre-empt the outcome of the debate by legislating restrictions that achieve their preferred result without reciprocity — on the theory that anything that limits nuclear arsenals, even unilaterally, is desirable in and of itself.

The two groups need to be brought together. So long as other countries build and improve their nuclear arsenals, deterrence of their use needs to be part of Western strategy. The efficiency of our weapons arsenals must be preserved. The program sketched here is not a program for unilateral disarmament. Both President Obama and Senator McCain, while endorsing this approach, also made it clear, in President Obama’s words, that the United States cannot implement it alone.

The danger posed by nuclear weapons is unprecedented. They should not be integrated into strategy as simply another, more efficient, explosive. We thus return to our original challenge. Our age has stolen fire from the gods; can we confine it to peaceful purposes before it consumes us?