The Return of Nuclear Escalation

Keir A. Lieber and Daryl G. Press

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Nuclear weapons once again loom large in international politics, and a dangerous pattern is emerging. In the regions most likely to draw the United States into conflict—the Korean Peninsula, the Taiwan Strait, eastern Europe, and the Persian Gulf—U.S. adversaries appear to be acquiring, enhancing, or threatening to use nuclear weapons. North Korea is developing intercontinental ballistic missiles that can reach the United States; China is doubling the size of its arsenal; Russia is threatening to use nuclear weapons in its war in Ukraine; and according to U.S. officials, Iran has amassed enough fissile material for a bomb. Many people hoped that once the Cold War ended, nuclear weapons would recede into irrelevance. Instead, many countries are relying on them to make up for the weakness of their conventional military forces.

Still, optimists in the United States argue that the risk of nuclear war remains low. Their reasoning is straightforward: the countries that are building up and brandishing their nuclear capabilities are bluffing. Nuclear weapons cannot paper over conventional military weakness because threats to escalate—even by a desperate enemy—are not credible. According to the optimists, giving credence to the nuclear bluster of weak enemies is misguided and plays squarely into their hands.

Unfortunately, the optimists are wrong. The risk of nuclear escalation during conventional war is much greater than is generally appreciated. The conundrum that U.S. adversaries face today—how to convincingly threaten escalation and bring a nuclear-armed opponent to a stalemate—was solved decades ago by the United States and its NATO allies. Back then, the West developed a strategy of coercive nuclear escalation to convince the Soviet Union that NATO allies would actually use nuclear weapons if they were invaded. Today, U.S. rivals have adopted NATO’s old nuclear strategy and developed their own options for credible escalation. The United States must take seriously the nuclear capabilities and resolve of its foes. It would be tragic for Washington to stumble into nuclear war because it discounted the very strategy that it invented decades ago.

NATO’S NUCLEAR PLAYBOOK

In the late 1950s, the forces of the Warsaw Pact, an alliance of the Soviet Union and seven other satellite states, outnumbered those of NATO in terms of manpower by about three to one. Up to that point, NATO’s response to Soviet conventional superiority had been simple. If the Soviets invaded Western Europe, the United States would launch an all-out nuclear bombing campaign against the Soviet Union. The message to Moscow was brutal but credible: the Soviets might have conventional superiority, but the next European war would not remain conventional.

But this strategy began to fall apart merely a decade into the Cold War. The Soviet Union was on the cusp of fielding a strong nuclear arsenal of its own, a vast improvement over the small and vulnerable force it had deployed up to that point. Soon, NATO’s strategy would no longer make sense. The alliance could not credibly threaten to respond to a conventional invasion with a full-blown nuclear strike on the Soviet Union because the Soviets would have the capability to retaliate in kind. During a war, NATO would face a lose-lose choice: lose a fight with conventional weapons or initiate a mutually catastrophic nuclear exchange. In other words, in the latter decades of the Cold War, NATO faced the same challenge that many U.S. adversaries face today: it had little hope of prevailing in a conventional war, and no hope of winning a nuclear one.

NATO found an answer to this problem. The alliance made plans to use nuclear weapons in the event of war, but in a different way. Instead of relying solely on the threat of a massive U.S. nuclear strike on the Soviet Union, NATO would respond to an invasion by using nuclear weapons coercively. That is, they would launch a few nuclear weapons—probably tactical ones, which have small yields and short ranges—against military targets to convince Soviet leaders that the war was spinning out of control, pressuring them to stop the invasion. Such a use of nuclear weapons could deliver a heavy blow to a Soviet advance, but more important, it would demonstrate to Soviet leaders that they were courting nuclear disaster. NATO had solved what had seemed to be an intractable problem: how to use nuclear threats to stalemate an enemy they could not beat at the conventional or nuclear level.

In contests of resolve, the side that cares the most has the advantage.

To back up this strategy, the United States deployed thousands of tactical nuclear weapons to Europe so that Washington could escalate in a manner that was distinguishable from an all-out strike on the Soviet Union. The alliance also created a “nuclear sharing” arrangement, whereby U.S. weapons based in Europe would be given to several NATO allies during a war, so that the countries the Soviet Union hoped to overrun would have their own nuclear defenses.

The details of NATO’s strategy evolved over time, but the core rationale remained constant. NATO would not keep its nuclear weapons holstered as its member states were being conquered; nor would it launch a suicidal nuclear strike on the Soviet Union. Instead, the alliance would escalate gradually and coercively, ensuring that the risks of continuing the conflict were too great for the Soviets to bear.

At the time, analysts criticized many aspects of NATO’s strategy. They argued, for example, that nuclear strikes on Soviet military targets would trigger retaliation against NATO’s forces, thus negating any advantage of using nuclear weapons in the first place. But the point of NATO’s escalation was not to change the military balance per se, but to use the shock of nuclear strikes to generate fear and compel the Soviets to accept a cease-fire. Other critics asked why NATO should expect that, once both sides escalated, the Soviets would be the party to blink first. But deterrence strategists noted that in a defensive war, the NATO allies would care more about defending their own freedom and territorial independence than the Soviets would care about waging a war of aggression. In contests of resolve, after all, the side that cares the most has the advantage.

Critics disapproved of NATO’s strategy for other reasons—threatening to start a potentially civilization-ending nuclear war seemed immoral, and assuming that escalation could be controlled once started appeared foolish. NATO leaders could not allay such criticisms, but the alliance nevertheless relied on the logic of deliberate escalation to defend itself from an otherwise overwhelming foe. NATO’s strategy made nuclear weapons the ultimate weapons of the weak, the perfect tool for holding off powerful rivals.

COPYCATS

This strategy of nuclear escalation did not disappear when the Cold War ended. Around the world today, several nuclear-armed countries that find themselves outmatched at the conventional military level lean on nuclear weapons to stave off catastrophic military defeat.

Pakistan is a prime example. Its principal adversary, India, has five times the population, nine times the GDP, and spends six times as much on its military. To make matters worse, most of Pakistan’s largest cities are less than 100 miles from the Indian border, and the terrain in the most likely corridors of an Indian invasion is difficult to defend. Unable to build sufficient conventional defenses, Pakistan’s leaders worry that a major war would lead to the destruction of its army and the seizure or isolation of its major cities. And so they rely on nuclear weapons to keep their next-door neighbor at bay.

Pakistan has approximately 170 nuclear warheads, a third of which are tactical. Pakistani officials have made clear that the country’s nuclear posture is designed to deter or halt an Indian invasion. The former head of Pakistan’s Strategic Plans Division, Lieutenant General Khalid Kidwai, explained in 2015 that “by introducing the variety of tactical nuclear weapons in Pakistan’s inventory, . . . we have blocked the avenues for serious military operations by the other side.” In May 2023, he reiterated that the purpose of Pakistan’s diverse arsenal is to give it a “strategic shield” to blunt India’s conventional military superiority. To this end, Pakistan has focused on being able to rapidly assemble, mobilize, and disperse nuclear weapons at the outset of any conflict. Of course, Pakistan could not hope to win a nuclear war against India—which has a comparable number of nuclear warheads and sophisticated delivery systems capable of retaliation—but Pakistan could inflict tremendous pain on its neighbor, coercing India to halt a conventional military campaign.

North Korea has adopted a similar strategy. Pyongyang’s conventional military is vastly outmatched by the combined forces of South Korea and the United States. North Korea’s army is large, but its military equipment is decrepit, and its troops rarely conduct training beyond simple small-unit exercises. Lacking the resources to compete militarily, Pyongyang leans heavily on its nuclear weapons. As the North Korean leader Kim Jong Un explained in 2022, although the primary mission of his country’s nuclear arsenal is to deter an attack, he would use nuclear weapons to repel an attack if deterrence failed. “If any forces try to violate the fundamental interests of our state, our nuclear forces will have to decisively accomplish [this] unexpected second mission,” Kim said.

U.S. and South Korean military planners, like their Indian counterparts, must now grapple with the same problem the Soviets once faced: how to capitalize on conventional military advantages against an enemy that may be willing to use nuclear weapons. The United States has more than enough nuclear weapons to respond to North Korean nuclear escalation, as leaders in Pyongyang surely know. But if there is a war on the Korean Peninsula, North Korea will be desperate. The country’s leaders fear succumbing to the same fate as recent rulers who lost conventional wars, such as Saddam Hussein in Iraq and Muammar al-Qaddafi in Libya, who were killed after being ousted. With their regime and lives on the line, Pyongyang’s leaders would face enormous pressure to start a perilous tit-for-tat nuclear exchange—at first striking targets in the region, and then possibly in the United States—to compel their opponents in Seoul and Washington to accept a cease-fire.

Unlike Pakistan and North Korea, China has declined to use nuclear threats to compensate for its conventional military inferiority relative to the United States. China’s reluctance to depend on nuclear threats is particularly notable given the high stakes of a major war over Taiwan. Defeat in such a conflict might lead to formal independence for the island—a major blow to China’s conception of its sovereignty. Perhaps more important, the loss of Taiwan would humiliate the Chinese Communist Party and could stoke a nationalist backlash or internal coup. Nevertheless, China has focused on improving its conventional military rather than readying its nuclear arsenal for wartime coercion. In fact, Beijing asserts that it will never be the first side in a conflict to use nuclear weapons.

To be clear, China’s nuclear doctrine is not as simple as it sounds. According to Chinese military documents, Beijing would consider exceptions to its no-first-use policy if China faced a major military defeat in a high-stakes conventional war. And Chinese strategists have considered how low-yield nuclear weapons could be used coercively. Additionally, around 2019 China began updating its nuclear forces in ways that would support a coercive strategy. It has increased the size, readiness, and diversity of its arsenal to increase its survivability; this would allow Beijing to initiate wartime escalation without fear that the United States could respond by destroying its nuclear force. Finally, China’s leaders could change their official stance during a war and use nuclear weapons if a conflict against the United States went badly. But as of now, China remains committed in its rhetoric to eschewing a nuclear first use and in addressing its military weaknesses by strengthening its conventional military power.

China’s current no-first-use policy aside, the pattern is dangerous to ignore: nuclear-armed countries that fear catastrophic military defeat frequently adopt escalatory doctrines to keep their enemies at bay. For NATO during the Cold War, Pakistan or North Korea today, and perhaps even China in the future, nuclear escalation on the battlefield makes sense if the only alternative is a regime-threatening defeat. Coercive nuclear escalation is a competition in pain—both inflicting it and suffering it—which is a type of conflict that invariably favors the desperate.

ALL IN

Russia is another country that embraces the strategy of coercive nuclear escalation. When the Cold War ended, the Western allies—suddenly freed from the fear of major military defeat in Europe—quickly soured on nuclear forces. Russia, acutely aware of its newfound conventional military inferiority, did the opposite, adapting NATO’s old ideas about nuclear escalation to Russia’s new circumstances.

Analysts debate the details of Russia’s current nuclear doctrine, but most agree that it calls for escalation to deter or stop the most serious military threats to Russian security. Like other conventionally weak but nuclear-armed countries, Russia has integrated into its conventional war-fighting plans and exercises many tactical nuclear weapons, including air-delivered bombs, cruise missiles, and short-range ballistic missiles. If the fighting in Ukraine shifts significantly in favor of Kyiv, and Russian President Vladimir Putin decides that defeat in Ukraine threatens his regime, Russia appears capable—and likely willing—to initiate a coercive nuclear war.

Putin has always portrayed the war in Ukraine as a core national security interest, based on historic territorial claims and the perceived threat of Ukraine’s membership in NATO. He has publicly framed the war in nearly existential terms. Perhaps most important, complete defeat in Ukraine would be humiliating and particularly dangerous to a leader who has built his power on a reputation for strength, acumen, and restoring Russian greatness. Preventing military catastrophe would be of paramount importance to Putin, and nuclear escalation would be one of his few remaining cards to play. No enemy army stands poised to invade Russia. But if Putin believes that complete defeat in Ukraine will lead to his being toppled—and killed or detained—he will likely see the stakes as sufficiently high to use nuclear weapons.

Russian leaders have made the links between the war in Ukraine and nuclear escalation clear. One of Russia’s most senior defense officials and former president, Dmitry Medvedev, said in July 2023 that Russia “would have to use nuclear weapons” if Ukraine’s counteroffensive succeeded in retaking Russian-held territory. “There simply wouldn’t be any other solution,” he said. Putin claimed in February 2023 that Western countries “intend to transform a local conflict into a phase of global confrontation,” adding that Russia “will react accordingly, because in this case we are talking about the existence of our country.” And in September 2022, he said that Russia would use “all means at its disposal” to defend its territorial annexations in Ukraine.

NATO’s strategy made nuclear weapons the ultimate weapons of the weak.

Perhaps these nuclear threats are mere bluffs aimed at convincing the West to end its support for Ukraine. In fact, some Western observers discount the plausibility of escalation, noting that if Russia’s military position in Ukraine starts to collapse, nuclear escalation would not solve Moscow’s problem. Ukraine’s military forces are dispersed, so even a handful of Russian tactical nuclear strikes would do limited damage to Kyiv’s forces. Moreover, Russian escalation would only make the Kremlin’s problems worse because NATO would probably respond with conventional attacks against Russian forces in Ukraine. In short, according to the skeptics, Russia’s nuclear threats are hollow.

Those who downplay Russia’s nuclear options misunderstand the logic of coercive escalation. Russia’s goal would not be to rectify the conventional military imbalance but to demonstrate in a shocking fashion that the war is spinning out of control and must be ended immediately. The aim would be to raise the prospect of a wider nuclear war and convince people and their leaders in the West that given what is at stake for Russian leaders, Moscow will keep inflicting pain to forestall defeat.

If Russian escalation triggered a large-scale conventional NATO attack on Russia’s forces in Ukraine, as many analysts expect it would, Moscow could just use nuclear weapons again—much as NATO would have done in the face of a Soviet invasion. Had the Soviet Union invaded a NATO member, the balance of wills would have favored NATO because the allies would have been fighting to protect their own freedom and territory. Now, if defeat in Ukraine endangers Putin’s regime, the Kremlin would have the most to lose. The reasoning behind escalation is brutal, similar to that for blackmail or torture. But self-interested leaders facing a defeat that could cost them their lives may have no other option.

To be sure, Russian nuclear escalation is only one possible course. The current battlefield stalemate may drag on until the two sides grudgingly agree to a cease-fire. Perhaps Russian forces will regain the initiative and seize larger swaths of Ukrainian territory. Or maybe Putin’s domestic opponents will remove him from power, opening the door to a better settlement for Ukraine. It is even possible that if Russia’s leaders order nuclear escalation, military commanders may refuse to carry it out, instead launching a coup to end Putin’s regime. The future of the conflict is uncertain, but the logic and history of the nuclear age is clear: when a conventionally superior army backs a nuclear-armed enemy against a wall, it risks nuclear war.

TABLES TURNED

Hawkish policy analysts suggest that the United States can stare down its adversaries’ nuclear threats if Washington has enough military power, a resolute mindset, and a strong nuclear deterrent. But those attributes will not deter an enemy that is cornered. The United States will be in grave danger if it underestimates the will of desperate, nuclear-armed adversaries.

The good news is that the Biden administration appears to understand the risk of escalation in the Ukraine war. Early statements made by U.S. President Joe Biden suggesting that Putin “cannot remain in power” have been replaced with more moderate rhetoric, and U.S. leaders have limited the kinds of weapons they provide Ukraine in large part to manage the dangers of escalation. Similarly, U.S. planners have encouraged their South Korean allies to consider wartime objectives far short of complete victory, to avoid pushing the Kim regime to the edge of nuclear war. For example, if North Korea launches a major artillery attack on South Korea, the wisest response may be to destroy or seize those artillery positions but not continue the campaign north to Pyongyang.

But it is impossible to know for sure how an enemy will react in war, especially because leaders are incentivized to misrepresent their actual redlines. Fighting nuclear-armed adversaries is a dangerous game of brinkmanship. There are military steps the United States can take to reduce these dangers. For potential conflicts on the Korean Peninsula and across the Taiwan Strait, the U.S. military should be developing strategies for waging conventional war in a manner designed to reduce the risks of escalation. For example, the U.S. military should minimize attacks that undermine an enemy leadership’s situational awareness and hold on power, such as strikes on national command-and-control networks, nuclear forces, and leadership targets themselves. Enemies who rely on nuclear weapons to stalemate U.S. military power will, of course, adapt as well; they will likely entangle the conventional and nuclear domains to prevent the United States from safely waging a conventional war. But the United States can make plans to escalate conventionally without threatening the survival of an enemy regime, thereby reducing the risk that a desperate leader will employ a nuclear weapon.

The United States must take the growing threat of coercive nuclear escalation seriously. After the Cold War, the United States became more ambitious in its foreign policy objectives. It spread Western political values and free markets and forged military ties around the world. But such objectives are opposed by nuclear-armed adversaries in China, North Korea, Russia, and perhaps soon in Iran. U.S. policymakers would be wise to not discount the potential power of their enemies. And if they need to be reminded of what their foes may be able to do, they need turn only to their own history.