The nuclear non-proliferation regime that helped contain the spread of nuclear weapons is crumbling. India and Pakistan became full-fledged members of the nuclear club in the spring of 1998 when they tested atomic weapons (India had previously conducted a “peaceful nuclear explosion” in 1974). North Korea detonated a nuclear device last October, and policymakers in Washington and Europe worry that Iran is using its civilian nuclear program to provide cover for a weapons program. Meanwhile, nuclear deterrence theory, the intellectual compass that guided our thinking about nuclear weapons and helped us navigate the Cold War, is condemned at best as “old thinking” and at worst as dangerously misleading.

This article addresses three questions: What is nuclear deterrence theory? Is nuclear deterrence theory still relevant, or is it a dangerous relic of the Cold War? If it is still relevant, then what does it tell us about some of the potential dangers posed by the spread of nuclear weapons? I argue that nuclear deterrence theory remains relevant, and it implies that the risk of states using nuclear weapons depends on two key factors being present at the same time. The first is a severe conflict of interest; the second is uncertainty about the balance of resolve between the states, i.e., about which state is willing to run the higher risk in order to prevail. The importance of the first factor is widely appreciated and understood, but the importance of the second is not.

What is Nuclear Deterrence Theory?

Nuclear deterrence theory can be seen as an effort to understand how political conflicts of interest play out in the shadow of nuclear weapons. The theory begins by recognizing that nuclear weapons do not eliminate political conflicts of interest. The United States and Soviet Union remained at odds after they acquired nuclear weapons; India and Pakistan continue to be divided over Kashmir.

Rather than eliminating political conflicts, nuclear weapons change the strategic setting in which those conflicts play out. Once two political adversaries acquire nuclear weapons and the means to deliver them, neither state can prevent its adversary from imposing horrendous destruction on it, should an adversary decide to do so. Thus, any crisis between these states poses a risk of spinning out of control and, ultimately, leaving each state far worse off than it would have been had it given in or acquiesced to its adversary’s original demands at the outset. For example, the original stakes of a crisis between the United States and the Soviet Union would hardly matter had that crisis ended in a massive nuclear exchange which left both societies in ruins. Likewise, the terms of a Kashmir settlement would seem unimportant after a nuclear exchange between India and Pakistan.

How does the risk of catastrophic escalation affect the way that political conflicts play out? How and to what extent can states exert coercive pressure on each other in order to further their interests in the shadow of such risk – be those interests to protect what they already have or to acquire more? A handful of scholars including Bernard Brodie, Hermann Kahn, Thomas Schelling, Glenn Snyder, and Albert Wohlstetter tried to answer these questions in the early years of the Cold War. Nuclear deterrence theory grew out of these efforts. Marc Trachtenberg’s “Strategic Thought in America, 1952-1966” in his History and Strategy provides an excellent overview of these efforts. Some of the ideas discussed here are developed at greater length in my article in International Security titled “Nuclear Deterrence Theory, Nuclear Proliferation, and National Missile Defense.”

Thomas Schelling saw that the risk of events spinning out of control transformed crises between nuclear-armed states into a kind of brinkmanship. The actions conventionally-armed states take during a crisis, e.g., mobilizing their forces and moving ships, exert coercive pressure primarily through their effects on the military balance between the states. In contrast, the actions nuclear-armed states take during a crisis, e.g., imposing a blockade as in the Cuban missile crisis or conducting a limited military probe, exert coercive power by raising the risk that the crisis will go out of control and end disastrously.

In a brinkmanship crisis, each state tries to induce the other to back down by taking steps that raise the risk that events will go out of control. This does not mean that states bid up the risk eagerly or enthusiastically. Although states may be very reticent to raise the risk, they may be still more reluctant to back down. Throughout a brinkmanship crisis, each state faces a series of terrible choices. It can quit, or it can decide to hang on a little longer and accept a somewhat greater risk, in the hope that its adversary will find the situation too dangerous and back down. If neither state backs down, the crisis goes on with each state effectively bidding up the risk until one eventually finds the risk too high and backs down, or until events actually do spiral out of control.

Brinkmanship crises, therefore, are contests of resolve, not of relative military strength. Resolve in turn depends on what is at stake in the crisis. The more a state has to gain by prevailing or the more it stands to lose if it backs down, the greater the risk of disaster it is willing to run in order to prevail, and the stronger its resolve.

A key point follows. What makes crises dangerous is the uncertainty about the balance of resolve, i.e., about which state is willing to run larger risks. Even if the stakes for both states were large enough so that each would pay a high price if it backed down, there would still be no escalation and no crisis if there were no uncertainty about the balance of resolve. The less resolute state would acquiesce to the more resolute state because the it knows that no matter how hard it pushes a crisis, the more resolute state would be willing to escalate still further. Indeed if the more resolute state has to, it is willing to push the crisis to the point where the risk exceeds the less resolute state’s resolve.