America’s Crisis of Deterrence

The United States and its allies are facing a crisis of deterrence. China is menacing Philippine vessels in the South China Sea and possibly readying its military for an invasion of Taiwan. Russia shows no sign of giving up its war in Ukraine. In the Middle East, Iran is threatening retaliation against Israel for the assassination of Hamas leader Ismail Haniyeh in Tehran, Hezbollah is ramping up its rocket strikes into Israel, and the Houthis continue to attack—and occasionally sink—commercial ships in the Red Sea. The compounding risks of Iranian missiles killing U.S. military personnel, of a Houthi strike on a U.S. Navy vessel, or of another sinking of a shipping vessel grow with time. Any of these events would force Washington to either get involved in a larger war or back down. Either option would reflect a failure of deterrence.

The foundations of deterrence theory lie in the Cold War writings of thinkers such as Thomas Schelling, who sought to formulate a strategy to deter a nuclear strike from the Soviet Union. Its central tenets—the stability produced by mutually assured destruction, the risks of escalation and the role of brinkmanship, and the value of signaling commitment and resolve—have proved useful for deterring nuclear-armed adversaries from conducting both nuclear and conventional attacks on other nuclear powers. They have been less useful for deterring attacks by nonnuclear powers. And when it comes to nonstate actors, deterrence theory has been downright useless.

Nowhere has this been more evident than in the Middle East in recent months, where Iran and its network of proxies have seemed willing to attack U.S. bases and service members, sink commercial ships, launch direct attacks on Israel, and possibly ignite a larger regional war. If Washington wants to keep deterrence in the region from eroding further, it will need to demonstrate a greater willingness to retaliate. Focusing on Hezbollah and the Houthis will not suffice; the only way to restore deterrence is by going after Iran. U.S. forces should retaliate in response to Iranian missile strikes that harm American military and civilian personnel. Washington should signal to Tehran that damage to U.S. ships or other vessels going through the Red Sea will be met with retaliation on Iranian assets or territory. The U.S. military should also position its assets in a manner that would enable it to continue to intercept Iranian air attacks—as it did when Iran fired a barrage of drones and missiles at Israel in April.

If U.S. officials deem pressuring Iran in these ways to be too risky, however, they could try to ride out the storm, wait for the war in the Gaza Strip and the current regional crisis to end, and turn their attention instead to China and Russia and the bigger picture. The Biden administration’s National Defense Strategy has made clear, after all, that the U.S. military needs to focus foremost on China. Such a choice would pose problems of its own: continued attacks on Israel, the constriction of international trade, and a diminished U.S. position in the Middle East. By understanding the requirements of deterrence, American leaders will be better positioned to judge whether that tradeoff is worth it.

MUTUALLY ASSURED DESTRUCTION

Before 1945, deterrence was not a major topic in the study of war. Its precepts are hard to find in the writings of thinkers such as Niccolò Machiavelli and Carl von Clausewitz. But beginning in the late 1940s, with the dawn of the nuclear age, strategists such as Schelling, Bernard Brodie, and Albert Wohlstetter began to formulate the bases of deterrence theory.

The foundation of nuclear deterrence is second-strike capability, meaning that either side can launch a devastating second strike in response to an attack from its adversary, a dynamic known as “mutually assured destruction.” China, France, Russia, the United Kingdom, and the United States possess this capability. Intercontinental ballistic missiles, submarines, silos, and mobile missile carriers make it impossible for any one of these powers to destroy an adversary without being destroyed itself.

Escalation is a paramount concern when both sides possess nuclear weapons. In his 1966 book, Arms and Influence, Schelling argued that any military action could lead to a series of actions and counteractions that could accidentally result in total disaster. “Just what would happen is a matter of prediction, or guess,” he wrote. “Military resistance tends to develop a momentum of its own.” Both sides bear risk. The United States cannot take an action against China or Russia without bringing upon itself the risk of things sliding out of control. As Soviet leader Nikita Khrushchev wrote to U.S. President John F. Kennedy at the height of the Cuban missile crisis:

We and you ought not now to pull on the ends of the rope in which you have tied the knot of war, because the more the two of us pull, the tighter that knot will be tied. And a moment may come when that knot will be tied so tight that even he who tied it will not have the strength to untie it, and then it will be necessary to cut that knot, and what that would mean is not for me to explain to you, because you yourself understand perfectly of what terrible forces our countries dispose.

Deterrence under mutually assured destruction thus requires a willingness to bear risk and to demonstrate that willingness. Signals that involve an action or bear a cost can be an indicator of the credibility of a commitment. Talk is cheap. An action signals better than words the stake the United States places in the issue at hand. Because of the risk of escalation, even a small step can be very dangerous and can signal great resolve. The placement of ground forces near an adversary’s forces, an aircraft buzzing a warship, or the passage of naval vessels near an adversary’s waters all bear a risk of escalation. American and Soviet decision-makers paid careful attention to such actions because they were aware of the dangers entailed.

SEND COSTLY SIGNALS

But Schelling and his contemporaries did not develop deterrence theory to explain how to deal with nonnuclear states—and when officials tried to apply it that way, the results were poor. In 1964 and early 1965, the Johnson administration attempted to apply Schelling’s thinking to North Vietnam, carrying out a series of graduated airstrikes to show that much greater damage would come if Hanoi did not back down. But things didn’t work out as Washington hoped. North Vietnam’s top leaders were unconvinced that the United States would overthrow them; they were willing to bear increasing losses to unite their country and continued to wage war in South Vietnam.

When confronting a nonnuclear power, the threat of mutually assured destruction is greatly reduced. A nuclear power faces little danger of nuclear disaster. This does not mean, however, that a nuclear power is free to apply force as it pleases. In some cases, such as in the U.S. invasion of Iraq in 2003, the absence of mutually assured destruction allows a nuclear power, such as the United States, to exert high levels of force with little concern about escalation. But in other cases, fear of an all-out conventional war against a nonnuclear state could prompt a nuclear adversary to get involved, as U.S. administrations worried might happen in the Korean War and the Vietnam War. And in some cases, the expenses and casualties of war may prove too high. Deterrence of a nonnuclear power is tricky because a nonnuclear adversary may assume that the United States is unwilling to bear the costs of an all-out conventional war.

The tools to deter China or Russia are unlikely to have the same effect on Iran or another nonnuclear state because in such scenarios the United States faces a much lower risk of nuclear retaliation. A move that would seem high risk if Washington took it against China or Russia would appear to be a cautious move if taken against Iran. Beijing or Moscow would likely perceive a signal such as the deployment of a U.S. Navy vessel near its waters as highly escalatory, an indication that the United States is willing to fight and risk accidents that could lead to shooting and nuclear considerations. But when the same tactic is applied against Iran, the United States faces no risk of nuclear disaster. Tehran, therefore, would likely interpret it as a sign of caution. When dealing with a nonnuclear state, a small step signals that either the costs or the benefits of a full war aren’t worth it; it does not convey resolve.

For this reason, the United States must take bigger steps when confronting nonnuclear opponents such as Iran. Of course, a major step, such as an airstrike against a target vital to a regime or the annihilation of an enemy’s navy, is not guaranteed to deter a nonnuclear power such as Iran. If the nonnuclear power is confident that the United States is not committed to military victory, then a large step could be seen as bluffing or as just another blow in an ongoing war of attrition. And if a large step is perceived as an indication of aggressive intent, such as regime change, a desperate nonnuclear power may, out of concern for its own survival, choose to escalate rather than make concessions. Ukraine would rather fight Russia than make concessions, believing that concessions would only strengthen Moscow’s hand and lead to conquest.

In a game of brinkmanship against a nonnuclear state, the United States must send costly signals that demonstrate commitment and capability, such as retaliatory strikes or the deployment of aircraft carriers and submarines for long periods. For example, the United States can shoot down an adversary’s aircraft or sink its vessels, as it did in Syria in 2017 and in the 1980s “tanker war” in the Persian Gulf. When an adversary launches an attack, the United States can send a strong signal by standing fast and repelling it. The defense of Israel against some 300 Iranian missiles and armed drones in April demonstrated the United States’ commitment to an ally. Israel and the United States intercepted nearly all of Iran’s missiles and drones, revealing Tehran’s capacity for retaliation against U.S. escalation to be weaker than previously thought. For more than a decade, Iran depended on its ballistic missiles to deter U.S. and Israeli airstrikes. As Frank McKenzie, who served as commander of U.S. Central Command from 2019 to 2022, states in his book, The Melting Point, a U.S. or an Israeli strike on Iranian nuclear facilities “would undoubtedly trigger a significant response from the Iranians” in “a bloody and violent ‘fires war’ where our bases and the cities of our regional friends will be targets.” The interceptions in April, however, cast doubt on the strength of Iran’s reputed deterrent.

PRESSURE THE PATRON

Deterrence theory is least helpful when addressing nonstate actors such as Hezbollah and the Houthis. Guerrillas lack the high-value military targets of states. And because guerrilla units are mobile and conceal themselves well, the missile systems they use are difficult to wipe out. Guerrilla leaders also have a high tolerance for personal risk, as many expect or even wish to become martyrs, which renders the threat of being killed in a U.S. airstrike a weak deterrent.

The United States has a history of crushing guerrilla and terrorist organizations through a combination of heavy surveillance, air and drone strikes, special operations, and coordinated raids with partner forces. That is how it defeated the Islamic State (also known as ISIS) and al Qaeda and held off the Taliban for a decade. Hezbollah and the Houthis are vulnerable to the same methods, and since they are close to the sea, the need for the United States to build expensive bases onshore would be reduced. But this approach takes time, requires a great deal of resources, and involves no small degree of destruction.

A more efficient way to deal with such groups would be to pressure their patron, Iran, by conveying that there will be consequences for continued missile and rocket attacks. This course of action is imperfect: Tehran will deny having influence over its proxies and accuse the United States of escalation, and Hezbollah and the Houthis have their own interests and may not listen to their patron. Still, both groups depend on Iranian support, and Tehran’s willingness to go to war on their behalf is far from assured, giving Iran considerable leverage to convince them to stop.

Signals that involve an action or bear a cost can be an indicator of the credibility of a commitment.

For that to happen, Tehran must be made to understand the repercussions it will face should its actions bring harm to U.S. forces. The United States must clarify its willingness to retaliate through actions rather than words—and small steps are not the way to go. Washington should make plain what risks Iran faces: all-out war and damage to Iran’s vital interests. The Biden administration should inform Tehran that it will intercept any missiles aimed at Israel, that it will avenge the loss of American life, and that Houthi missile attacks in the Red Sea must stop. Before an errant missile strikes a ship, every Houthi antiship missile launch should be matched with a U.S. action against Iran. This could take the form of surveillance inside territorial waters, warning shots on Iranian vessels, or boardings of Iranian commercial vessels that might be smuggling arms. The Pentagon should also think of creative ways to show that Iranian military assets can immediately be damaged, such as through cyberwarfare or special operations. Washington must reinforce the message by sending offensive forces to the Middle East. President Joe Biden’s recent deployment of two aircraft carriers, guided missile destroyers, F-22 fighters, and a guided missile submarine are welcome moves.

Finally, the United States should continue to stand fast in the missile defense of Israel. Doing so demonstrates commitment and limits Iran’s options. Owing to the success of their interceptions of Iranian missiles, the United States and Israel are in a stronger position now to deter Iran.

Of course, if the risks of this approach appear too high and the resources required would distract from other priorities, the United States could back off. It could say nothing about missile strikes on Israel and, to alleviate the risk of accidental escalation, remove its naval presence and discourage commercial traffic from going through the Red Sea. It would not be the first time Israel has endured Hezbollah rocket strikes. Nor would it be the first time that the Red Sea has been closed to commercial traffic. The Suez Canal was closed from 1967 to 1975 amid wars between Egypt and Israel. The United States could accept a similar situation until the Gaza crisis abates. The potential costs of that approach include more attacks on Israel, a reduction in international trade, and a weakened U.S. standing in the Middle East. Yet if the overriding goal is to avoid being bogged down in the Middle East while defending U.S. interests and thwarting aggression in the region, Washington must recognize that deterrence demands accepting uncomfortable risks.