Welcome to the New Era of Nuclear Brinkmanship

The Ukraine war is the first great-power nuclear crisis of the 21st century — and it won’t be the last. Since February 2022, Russian President Vladimir Putin has rattled his nuclear saber in hopes of isolating Ukraine and intimidating it into submission. The US has responded by threatening Putin with terrible reprisals if he uses nuclear weapons, and by cooperating with Western allies to sustain Ukraine despite Moscow’s threats. The nuclear risk-taking is both a throwback to Cold War-era superpower crises and a preview of what lies ahead.

America is immersed in sharp security competitions with Russia and China. For both countries, nuclear weapons are central to their programs for regional expansion and their preparations for a potential showdown with the US. As Washington and its rivals joust for influence around the Eurasian periphery, they will come face-to-face in crises where nuclear weapons cast ominous shadows. To safely navigate the next great-power nuclear crisis, America will need to learn the lessons of this one.

At first glance, the lesson might seem to be that nukes don’t matter. Nuclear weapons haven’t saved Moscow from its Ukrainian quagmire. They haven’t deterred Kyiv from fighting back fiercely, or prevented the US and its allies from waging a ferocious proxy war that has killed tens of thousands of Russian invaders. If nuclear weapons can’t give Russia a decisive edge against a smaller, weaker neighbor, then are they really so important?

The short answer is yes. Nuclear weapons have profoundly influenced the war in Ukraine, albeit in subtle and sometimes hidden ways.

Without nuclear weapons and nuclear threats, Russia might well have lost the war by now. And without the backing of a US nuclear arsenal harnessed to the security of Washington’s allies, Ukraine might have lost, because Russia could have more brutally coerced the countries whose aid is keeping Kyiv alive. Uncomfortable as it may be to recognize, the primary lesson of the Ukraine war is that nuclear coercion will be essential to prevailing in the rivalries that define our age.

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As Russian troops streamed into Ukraine in February 2022, Putin issued a chilling warning: “Whoever tries to impede us, let alone create threats for our country and its people, must know that the Russian response will be immediate and lead to the consequences you have never seen in history.” This was the first of many such threats Putin would issue, as part of his strategy to use nuclear coercion in the service of conventional aggression.

Since taking power two decades earlier, Putin had rebuilt Russia’s conventional military as a sword to be used against its smaller neighbors, while modernizing its nuclear forces as a shield against interference by a meddling superpower. The first time Putin invaded Ukraine, in 2014, he apparently prepared to raise Russia’s nuclear alert status to make sure Washington and its NATO allies stayed passive.

Putin’s vague nuclear threats in February 2022 were intended, likewise, to safeguard the spoils from what he thought would be a quick and easy victory. When the war went bad during late summer and fall, Putin again invoked Armageddon in a bid to freeze a deteriorating situation.

Putin and other Russian officials hinted at the use of nuclear or chemical weapons on the battlefield. In September, as Kyiv’s forces were liberating areas around Kharkiv and assaulting occupied Kherson, Putin announced plans to annex four Ukrainian regions. Russia would defend this land “with all the powers and means at our disposal,” he declared, adding that America’s use of nuclear weapons against Japan in 1945 had created a “precedent” others might follow.

These warnings caused concern in Washington that Putin might indeed use nuclear weapons if the alternative was the collapse of his military and, perhaps, his regime. According to National Security Adviser Jake Sullivan, US officials threatened unspecified “catastrophic consequences” if Russia went nuclear. Other countries, namely China and India, also nudged Putin back from the brink. The crisis passed, with Putin saying there was “no need” for dramatic measures, but the nuclear menace hasn’t gone away.

Russia has now announced plans to deploy nuclear weapons to neighboring Belarus. Putin’s toadies have warned that “every day” Western powers aid Ukraine “brings the nuclear apocalypse closer.” Russian analysts, presumably writing with the tolerance if not necessarily the support of the Kremlin, have argued that Moscow must wage limited nuclear war against the West to get its way.

Nuclear weapons are the most devastating tools humanity has created. Since February 2022, Russia has been trying to exploit the fear they sow to end this conflict on its own terms.

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One might be forgiven for thinking it hasn’t worked. Putin’s bluster hasn’t stopped the West from giving Ukraine money arms, and intelligence. US officials publicly say their goal is to “weaken” Russia by subjecting it to catastrophic losses.

Nor did Putin’s threats freeze the conflict: To this day, Ukraine continues to assault the “Russian” territory Moscow annexed. Those threats haven’t even prevented Kyiv from attacking Russia itself, by bombing airfields, conducting drone strikes on Moscow, and sponsoring cross-border raids. Whenever Putin talks about employing nuclear weapons, in fact, he faces condemnation by the West and opposition from his own allies and neutrals — raising the prospect that using Russia’s arsenal would complete Russia’s isolation.

If events in Ukraine are any guide, nuclear weapons aren’t that effective for consolidating territorial conquest, if that conquest is deemed illegitimate by one’s enemy and most of the world. They’re hard to use in ways that make a decisive difference on the battlefield but aren’t so devastating that they elicit international opprobrium out of proportion to the military gain. Nuclear weapons may be good insurance against invasion, but they aren’t a foolproof guarantee that a country fighting for survival won’t hit back with attacks on a nuclear-armed aggressor’s soil. The war, in all these respects, has underscored the difficulty of using nuclear weapons to underwrite aggression, especially against an opponent that refuses to give in because it believes the stakes are existential.

The effects of nuclear weapons in Ukraine have been limited — but they are hardly nonexistent. In fact, Russia is successfully using nuclear weapons to coerce the US. And the US is using its own nuclear arsenal to coerce Russia right back.

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The best way to isolate this impact is to consider two counterfactual scenarios. First, imagine a world in which the US had nuclear weapons and Russia didn’t. In this world, America would probably be less restrained in aiding Ukraine, because it would have less anxiety about a devastating Russian riposte.

US aid to Ukraine has been generous but carefully circumscribed. Washington has discouraged Kyiv from attacking Russian soil (especially if those attacks use US weapons), even though Ukraine has every legal and moral right to do so. President Joe Biden has held back tools, such as ATACMS rockets, that can reach into Russia, largely for fear of breaching Putin’s red lines. America has been ambivalent about the idea of Ukraine forcibly retaking Crimea, encouraging it to use a squeeze-and-negotiate strategy instead. Wisely or not, Washington has asked Ukraine to fight with one arm behind its back, out of concern about entering a perilous spiral with a nuclear-armed regime.

If Russia lacked nuclear weapons, the US would lack its single most powerful reason for this restraint. It would also have greater incentive to intervene directly, the surest and speediest path to Russian defeat.

If this seems improbable — Biden has made avoiding war with Russia the “north star” of his policy — it is at least partly because we have become so accustomed to the specter of mutual assured destruction. Absent that danger, would the US really tolerate a ghastly forever war in Europe’s second-largest country? One that has roiled global food and energy markets, fomented violent instability on NATO’s doorstep, and threatened the vital norm against territorial aggrandizement by force? One that had the potential to shatter the strategic equilibrium in Western Eurasia had Putin’s gambit succeeded? One that so evoked the 20th century’s darkest patterns of aggression and atrocity that some of America’s European allies compared the invasion to Hitler’s destruction of Czechoslovakia before World War II?

America has fought to turn back lesser challenges to regional and global stability than this — its interventions in the Persian Gulf and Balkans in the 1990s, for instance. If Washington and its allies had only to defeat a Russian conventional military that was already bogged down and degraded, they might well have done so, knowing that Putin had few good options to respond.

Nuclear weapons have thus played a vital holding-the-ring function for Moscow, allowing it to fight a constrained Ukraine rather than a larger Western coalition. Nukes haven’t won the war for Putin. They have, however, helped him avoid defeat.

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Now consider a second counterfactual: One in which Russia had nuclear weapons and the US and NATO did not. In this scenario, Ukraine might well be struggling to keep fighting, because Moscow would be far better positioned to intimidate the countries sustaining it.

The amount of Western interference Moscow is tolerating in its fight against Ukraine is rather remarkable. The US and its allies have turned countries just across the border from Ukraine, especially Poland, into hubs for the delivery of vital weapons and training grounds for Kyiv’s forces.

Biden has erected a powerful shield — a nuclear shield — around these activities, by pledging to defend “every inch” of NATO territory from Russian attack. If Russia possessed could make nuclear threats that Washington and its allies could not answer, that shield would be much weaker.

It seems doubtful that a Russia possessing this advantage would simply watch as its army was bled to death by a ceaseless flow of materiel from abroad. During the Vietnam War, the US attacked communist sanctuaries in Laos and Cambodia. In Afghanistan during the 1980s, Soviet forces periodically crossed into Pakistan to raid insurgent camps. Absent the strategic stalemate created by US nuclear weapons, Putin would surely be tempted to do likewise. And absent America’s extended nuclear deterrent, countries on NATO’s eastern front would be less likely to risk this scenario by incurring Putin’s wrath. Case in point: Earlier this year, Germany wouldn’t even permit re-export of its Leopard tanks to Ukraine without the explicit backing of its nuclear-armed superpower ally.

Russia’s inability to sever Ukraine from its Western backers doesn’t show the uselessness of nuclear weapons. It shows that nuclear coercion is working both ways. Nuclear weapons have probably helped rescue Ukraine from defeat — while also making Eastern Europe safer for the Kremlin’s brutal war.

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One lesson from Ukraine, then, is that nuclear weapons — even when they aren’t used in battle — powerfully shape what happens in an ostensibly conventional fight. Another lesson is that the effects of these weapons are psychological at their core.

Russia’s nuclear capabilities haven’t changed since February 2022. But their impact on Western policy has changed, albeit subtly. Over the last 18 months, the US and its allies have gradually become bolder in giving Ukraine weapons — main battle tanks, F-16s, longer-range British and French missiles — that they were once more hesitant to provide. One reason for this is that Putin’s nuclear threats have been slowly losing credibility: The fact that he has so frequently brandished his bombs, without ever using them — even when Russian defenses around Kharkiv were crumbling — has caused Western officials to shed some earlier fear of escalation.

This dynamic raises an intriguing question: What would have happened had the West simply ignored Putin’s nuclear threats from the outset? In March 2022, Russian forces were stuck outside of Kyiv. The application of Western airpower would have devastated Putin’s overextended army. Putin’s only real recourse would have been limited nuclear strikes against targets in Ukraine or NATO countries in Eastern Europe.

Perhaps Putin would have chosen this option. Or perhaps he would have decided that losing a conventional war was better than starting a nuclear one. It’s hard to know what the US should have done in this instance for the same reason nuclear statecraft is always vexing: It requires us to climb inside the heads of our opponents and guess what they will do when the decisive moment comes, knowing that the price of guessing wrong could be utter catastrophe.

Yet the question requires asking, because the contest in coercion isn’t over. Barring some unexpected breakthrough on the battlefield, Ukraine will likely struggle to expel Russian forces without more — and more sophisticated — Western aid than it has received to date. It may not be able to convince Putin to call off the conflict until it has shown it can bring the fighting home to Russia in a more sustained, serious and politically damaging way.

It is even possible that at some point the US will have to choose between intervening militarily or letting Ukraine become a failed state, exporting refugees and insecurity to Europe for years to come. At some point, in other words, the US may be forced to test Russia’s red lines more aggressively or settle for an outcome that allows Putin to claim a very ugly, very partial victory.

An earlier generation of American policymakers would have understood this imperative well. During the early Cold War, the US repeatedly found itself in high-stakes nuclear crises with the Soviet Union. And it repeatedly threatened to wage nuclear war rather than see Moscow or its allies conquer Taiwan’s offshore islands, dislodge the Western powers from Berlin, or otherwise destabilize the global order.

“If you are scared to go to the brink, you are lost,” a respected secretary of state, John Foster Dulles, once explained. To modern ears, Dulles might sound like a maniac. At the time, most Americans agreed with him.

Perhaps America will be spared similar dilemmas in this round of global rivalry. But don’t count on it. In fact, if Ukraine is a precedent for how America handles crises with nuclear-armed great powers, the US is in big trouble in the Western Pacific.

One of the most important questions raised by this war is what Chinese President Xi Jinping makes of it. Maybe Xi has been impressed by the cohesion of the West and the subpar performance of an autocratic military — lessons that would reinforce the peace in the Taiwan Strait. Or maybe he has learned something different: That America won’t fight even a conventional war against a nuclear-armed rival.

Biden has said as much. “We will not fight a war against Russia in Ukraine,” he declared in March 2022, because that would mean “World War III.” It’s not clear why the US would be more willing to risk nuclear war for Taiwan — another strategically important but distant democracy — than it was for Ukraine. It is clear that America’s strategy in Ukraine — provision of supplies and other support short of war — won’t work as well in sustaining an island that lacks friendly countries next door. So if the US won’t intervene directly if China attacks, say goodbye to a free Taiwan.

Biden understands this: It’s presumably why he has said, several times, that the US won’t stand aside if China attacks. But would it really be so crazy for Xi to conclude, with Ukraine in mind, that America’s actions speak louder than its words? Nuclear statecraft is replete with ironies. One of them is that deterring a future war in the Western Pacific may require convincing China not to draw too many conclusions from the current war in Ukraine.