Deterrence isn't what it used to be. In the second half of the twentieth century, it was the backbone of U.S. national security. Its purpose, logic, and effectiveness were well understood. It was the essential military strategy behind containing the Soviet Union and a crucial ingredient in winning the Cold War without fighting World War III. But in recent decades, deterrence has gone astray, and U.S. defense policy is worse for the change.
Since the Cold War ended, the United States has clung to deterrence where it should not have, needlessly aggravating relations with Russia. More important, it has rejected deterrence where it should have embraced it, leading to one unnecessary and disastrous war with Iraq and the risk of another with Iran. And most important, with regard to China, Washington is torn about whether or not to rely on deterrence at all, even though such confusion could lead to a crisis and a dangerous miscalculation in Beijing.
Mistakes in applying deterrence have come from misunderstandings about the concept itself, faulty threat assessments, forgetfulness about history, and shortsighted policymaking. Bringing these problems into focus can restore faith in deterrence where it has been lost, lower costs where the strategy has been misapplied, and reduce the danger of surprise in situations where the risk of conflict is unclear.
Deterrence is a strategy for combining two competing goals: countering an enemy and avoiding war. Academics have explored countless variations on that theme, but the basic concept is quite simple: an enemy will not strike if it knows the defender can defeat the attack or can inflict unacceptable damage in retaliation.
At best, applying deterrence when it is unneeded wastes resources. At worst, it may provoke conflict rather than hold it in check. And even when deterrence is appropriate, it might not work-for example, against an enemy who is suicidal or invulnerable to a counterattack. Thus, it is more useful against governments, which have a return address and want to survive, than against terrorists who cannot be found or who do not fear death. Deterrence is also a weak tool in the increasingly important realm of cyberspace, where it can be extremely difficult to be absolutely sure of an attacker's identity.
When the United States does choose to apply deterrence and is willing to fight, the deterrent warning must be loud and clear, so the target cannot misread it. Deterrence should be ambiguous only if it is a bluff. One of the biggest dangers, however, comes in the reverse situation, when Washington fails to declare deterrence in advance but then decides to fight when an unexpected attack comes. That kind of confusion caused the United States to suddenly enter both the Korean War and the Gulf War, despite official statements in both cases that had led the aggressors to believe it would not.
Deterrence is not a strategy for all seasons. It does not guarantee success. There are risks in relying on it and also in rejecting it when the alternatives are worse.
To Moscow, it must seem that the Cold War is only half over, since the West's deterrence posture, although muted, lives on. During the Cold War, deterrence was vital because the Soviet threat seemed huge. Moscow's military capabilities included some 175 divisions aimed at Western Europe and close to 40,000 nuclear weapons. Soviet intentions were much debated, but they were officially assumed to be very hostile. The West's response was to deploy ample military counterpower via nato and the U.S. Strategic Air Command. And for more than 40 years, deterrence held. Despite tense crises over Berlin and Cuba and proxy conflicts in the Third World, Moscow never dared unleash its forces directly against the West. Doves doubted that so much deterrence was necessary, but hawks were reassured that against a potent threat, deterrence did not fail.
Yet implicit deterrence persisted after the West's victory because of demands from members of the old Warsaw Pact that joined nato, the retrograde politics of the post-Soviet Russian state, and sheer force of habit. …