Deterrence After Ukraine—A Critical Analysis

On February 24th, Russia invaded Ukraine with the explicit goal of eliminating its existence as an independent country. Why was Russian President Vladimir Putin not deterred by the risk of a response from the West/NATO? This question requires a review of the fundamentals of conventional deterrence, neglected by the West during the Cold War and virtually abandoned since the fall of the Soviet Union. It also calls for a re-examination of the link between conventional and non-conventional (chemical, biological, radiological, and nuclear) deterrence.

The US Department of Defense defines deterrence as “the prevention of action by the existence of a credible threat of unacceptable counteraction and/or belief that the cost of action outweighs the perceived benefits.” Or, as Dr. Strangelove (Peter Sellers) put it in Stanley Kubrick’s 1964 film of the same name, “Deterrence is the art of producing in the mind of the enemy the fear to attack.” In short, effective deterrence rests on a cost-benefit calculation. It is achieved when an actor refrains from an aggressive action because he has been made to understand that it will be met with equivalent or greater force, and that the cost of aggression will nullify any benefit accrued. Its defining characteristic is the successful threat of force—not the actual use of force.

Practitioners, analysts, and scholars differentiate between two main categories of deterrence:

• Deterrence by denial: An actor elects not to undertake an action because he believes a second party has taken, or will take, steps to ensure that it will fail to achieve its desired result.
• Deterrence by punishment: An actor elects not to undertake an action because he fears it will trigger a response from a second party that will impose unacceptable costs.

Deterrence by denial is mainly relevant to defense of the homeland through a system of theater defense, anti-ballistic missiles, and protection of the civilian population. NATO deterrence of a conventional attack on Europe relies on deterrence by punishment. Once an adversary has ignored the threat and launched its attack, deterrence has, ipso facto, failed. When deterrence has either failed or has not been attempted (for example, when the adversary has launched a surprise attack), an actor must then rely on “compellence”: the threat or use of force to cause an adversary to change behavior in which it is already engaged.

Before the invasion, a number of pundits on the Left and Right were confidently predicting that it would never happen, and that Western intelligence agencies and media outlets who reported otherwise were warmongering. Then, when the invasion duly began, a number of the same pundits declared Putin “unbalanced” or “mad” or “irrational”—someone who could not have been deterred by a rational cost-benefit analysis in any case. This kind of reasoning is a defense mechanism employed by individuals and organizations looking to explain away their own failures of judgment. But, as Shakespeare had Cassius observe, “The fault, dear Brutus, is not in our stars, but in ourselves, that we are underlings.”

The failure of deterrence in Ukraine

NATO’s conventional deterrence has been tested by the Ukraine crisis and found wanting. While previous Russian military actions caught the West by surprise, the invasion of Ukraine was anticipated by Western intelligence communities. This led the president of the United States to try to deter Russia by releasing intelligence, announcing Russia’s intention to invade, and threatening retribution with sanctions and condemnations if it did so.

The Biden administration evidently hoped that fear of international isolation would outweigh any advantage Russia might achieve by invading Ukraine—that a combination of “carrots” (fresh talks on missile deployments and troop exercises) and “sticks” (the threat of further financial sanctions) would deter Putin from continuing his brinkmanship on the Ukrainian border. Russia, however, was not impressed either by the carrots, which it viewed as a ploy to entangle Moscow in endless negotiations, or by the sticks, which it calculated would be tolerable.

The Kremlin did not need Biden’s January statement about a “minor incursion” to know that the US would not counter a Russian invasion of Ukraine with military force. The history of American attempts to deter rogue regimes (Syria from using chemical weapons, Iran from launching missile attacks on US forces and allies in Iraq, North Korea from conducting missile and nuclear tests) persuaded Putin that the US was highly unlikely to retaliate even to direct attacks. The only possible American reaction would be enhanced sanctions, the severity of which would depend on the scale of the invasion. Moscow calculated that, in a conflict over an issue that one party sees as its vital interest and the other party sees as a liability without really knowing what to do, the first party wins.

So, no attempt was made by NATO to deter Moscow with the threat of military force. To the contrary, it was Russia’s deterrence that proved to be successful. Western leaders consistently reassured their domestic audiences that there would be no military intervention on the part of NATO or the US. In every speech he delivered on the subject, President Biden reiterated that the US “will not send troops to Ukraine” and “will not fight Russia,” but would “defend the borders of NATO” should it be required to do so. Because Ukraine is not a member of NATO, it is not covered by Article 5 of the NATO treaty. One may argue that since military deterrence was explicitly ruled out, it did not fail. Nevertheless, the deterrence measures that the West did employ clearly did—Russia invaded Ukraine.

Putin was undeterred by the West’s messaging, not because he misunderstood it, but because he understood it perfectly. The expected costs of an invasion, he decided, were not sufficient to outweigh the “historic” goal of restoring Ukraine to Russia. Even Biden’s warning of Putin’s intention to erode Western democracies/NATO backfired, because it flattered Putin’s belief that Russia ought to the chief geopolitical nemesis of the United States. For years—and certainly since the Biden administration cold-shouldered him and pressed ahead with its pivot to Asia—Putin has felt that Russia (and he himself) had been marginalized in the international agenda. The very effort to deter him restored him to the international stage.

Putin’s miscalculation was not made vis-à-vis the West but in regards to Ukraine itself. He under-estimated the resilience of the Ukrainian leadership, military, and people, and he over-estimated the readiness and capability of his own military. He had expected a Blitzkrieg or even an “Anschluss” that would culminate in welcome parades cheered by hundreds of thousands of Ukrainians, happy to return to Mother Russia. This mistake had nothing to do with Western deterrence—it was a failure of the intelligence assessments informing Russian decision-making.

Once deterrence failed, the West’s attempts to stop the war refocused on compellence. However, this effort was based on the same suite of political and economic sanctions that were threatened in order to achieve deterrence. Why should threats that failed to deter Putin from invading Ukraine be any more effective in forcing him to reverse his strategy and retreat? As the invasion continues, the price of a policy reversal grows, but the price of maintaining its course (sanctions) remains the same. In addition to the practical military and economic costs imposed by battlefield losses, Russia finds itself hostage to the “sunk cost fallacy.” So, the severity of Western threats will require a corresponding escalation to achieve compellence.

Conventional war with a nuclear topping

“Whoever tries to hinder us,” Putin announced as Russia launched its invasion, “should know that Russia's response will be immediate. And it will lead you to such consequences that you have never encountered in your history.” This ominous but ambiguous statement appeared to indicate that Western interference would be met with nuclear retaliation.

Three days later, Putin ordered his armed forces to raise the alert status for Russia’s nuclear arsenal to “special regime of combat duty.” This wording had never been used before, so there was some confusion about its precise meaning. The official levels of Russian defense readiness condition are: 4. Regular Combat Readiness—the army of the peacetime; 3. Elevated Combat Readiness; 2. Danger of War; 1. Full Combat Readiness—the highest level. The deputy director general of the Royal United Services Institute told the Press Association:

I haven’t seen any reporting of changes in Russian nuclear forces postures. Obviously I don’t have access to classified intelligence but I haven’t seen reports as such. So it’s not clear how that changes. It may be something to do with the particular authorisation mechanisms between the president and the nuclear forces or it may be nothing at all. What is clear is that this is designed to be something that we need to listen to. It’s designed to be a reminder that Russia is a nuclear weapons power.

This is part of Russian psychological warfare, and a form of compellence intended to halt Western provision of military support to Ukraine. By putting his nuclear forces on alert, Putin effectively challenged the US to respond in kind. And when it did not, he proved to his elites that his brinkmanship was working. Indeed, the American response downplayed the Russian move.

The connection Russia made between the conventional war in Ukraine and the possible use of nuclear weapons reflects an asymmetry in the way Russia and the US understand and employ nuclear deterrence. The US has never developed a doctrine that envisaged the use of tactical nuclear weapons in a conventional conflict. The raison d'être of the US nuclear arsenal was to deter an existential threat by another nuclear power to the US or to countries to whom the US has provided extended assurances. Since the end of the Cold War, the United States has dramatically reduced its tactical nuclear weapons, and today keeps only a limited number of forward-deployed nuclear weapons in Europe, plus a small number of nuclear weapons stored in the United States, available for global deployment to allies and partners in support of extended deterrence.

The USSR and its successor Russia, on the other hand, developed a doctrine that provided for the use of tactical nuclear weapons to de-escalate or end a conventional conflict in which Russian conventional forces are unable to make progress. NATO would then be compelled to end hostilities by the fear that further escalation could result in total strategic nuclear war. The US Defense Department’s 2018 Nuclear Posture Review states explicitly that:

Russia may also rely on threats of limited nuclear first use, or actual first use, to coerce us, our allies, and partners into terminating a conflict on terms favorable to Russia. Moscow apparently believes that the United States is unwilling to respond to Russian employment of tactical nuclear weapons with strategic nuclear weapons.

Cold War deterrence

The Ukraine crisis is an extension of the Cold War conflict between the Soviet Union and the West, and in that sense, it constitutes the first test of NATO’s conventional deterrence towards Russia in Europe. Before the Soviet Union acquired a nuclear weapon, NATO had already been established with the aim of deterring conventional Soviet aggression against Western Europe. In the 75 years since, none of the Kremlin’s acts of belligerence—against Soviet-bloc countries such as Hungary (November 1956) or Czechoslovakia (August 1968), or in the post-Soviet era against Georgia (August 2008) or the Crimean Peninsula (February/March 2014)—caused NATO to take political or military steps to deter Russian aggression.

In retrospect, the Cold War was far less stable than it seemed to be at the time, and the risk of nuclear war was far higher than the conventional wisdom indicates. As mutual deterrence evolved, it provided an “umbrella” for conventional and low-intensity conflicts. Furthermore, while the leaderships of the United States and the Soviet Union took most of their respective decisions on the basis of a cost-benefit calculus and an assessment of the compatibility between ends and means, the perception of reality on which these decisions were based was profoundly influenced by cultural perceptions. In many cases, a decision to back down from conflict was not due to the deterrent signals that the other side transmitted (these were frequently not even received or were misinterpreted) but to other factors that the adversary was not even aware of.

A key element of stability during the Cold War was the concept of extended assurances—a leftover from the shock of World War II, which underscored the sense of mutual dependence between the New World and the Old. It was based on the view of successive post-war American administrations that the role of American nuclear weapons was not only the defense of the United States against a possible Soviet attack, but the “defense of the Free World.” Even so, when French President Charles de Gaulle asked President Kennedy in May 1961 if Americans would be prepared to “trade New York for Paris,” the reply was not reassuring enough to dissuade de Gaulle from developing France’s own nuclear deterrent. As a contemporaneous memorandum of the conversation noted: “If the General himself, who has worked together with the United States for so long, could question American firmness, Mr. Khrushchev can question it also.”

Since the Cold War never escalated into a nuclear conflict, the concept of extended nuclear deterrence was never put to the test. However, the credibility of extended assurances was implicitly based on the US commitment to support its allies, not only in a nuclear conflict but in conventional conflicts as well. This was the strategic logic behind the launching of Operation Desert Storm to liberate Kuwait, US intervention in Iraq and Syria against ISIS, and a continuing US presence in the Middle East and Asia.

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Cold War 2.0 and the democracy dilemma

Conventional deterrence has been marginalized by the focus on nuclear deterrence since the start of the Cold War, but the Ukraine conflict demonstrates that a local conventional threat in Europe can pose a strategic challenge. Since it cannot be deterred by the threat of nuclear retaliation, it must be met with a robust conventional deterrence.

Cold War 2.0 has been with us for at least a decade, but there have been few changes in NATO’s formal doctrine of deterrence. At the same time, there have been significant changes in the attitudes of Western publics towards the use of force, threats of force, and the legitimacy of even threatening to use nuclear weapons within a framework of deterrence. These changes—and their practical manifestation during the Ukraine crisis—have clarified that the US will certainly not trade New York for Paris. This has become the new framework for any discussion of deterrence going forward.

With the exception of the military action undertaken after 9/11, there has been a gradual but steady decline in US popular support for intervention in foreign conflicts—and certainly for the use of nuclear weapons—since the Vietnam War. In the past, nuclear policy was an esoteric field of military strategy of no interest to most of the American public. The growing aversion in the US to conflict of any kind—no matter how just the cause—makes any use of nuclear weapons unthinkable. Since the dawn of the first nuclear age, philosophers and religious leaders have asked: If the use of nuclear weapons is fundamentally immoral, then isn’t threatening to use them in order to deter an enemy equally immoral? This debate has affected the practical doctrine of the West, and threatening to use nuclear weapons is now almost as taboo as using them.

The dilution of the American commitment to use nuclear weapons in response to a nuclear attack on an ally to whom the US has accorded extended assurances began with the Obama administration’s Nuclear Posture Review in 2010:

The U.S. nuclear posture has a vital role to play in regional security architectures. Proliferating states must understand that any attack on the United States, or our allies and partners, will be defeated, and any use of nuclear weapons will be met with a response that would be effective and overwhelming. The President, as Commander-in-Chief, will determine the precise nature of any U.S. response. [My emphasis]

The Trump administration’s NPR in 2018 made this retreat from previous commitments even more explicit: “The United States wishes to stress that it would only consider the use of nuclear weapons in extreme circumstances to defend the vital interests of the United States or its allies and partners.” The result has been to significantly reduce the credibility of US extended nuclear assurances.

A major vulnerability of democratic countries is that they cannot project separate messages to their own domestic audiences and to the enemy. The leader of a democratic country cannot convince an adversary that he is willing to use force if public opinion and high-ranking members of the political elite openly oppose it. While an adversary may not need proof that a country will resist if it is attacked directly, extended deterrence for allies is a game of poker. When the president of the United States tells his constituency that “we will not fight Russia” in a speech condemning the invasion of Ukraine, he knows that Russia is also listening.

Tailored deterrence

When the invasion of Ukraine began, Western pundits bemoaned the failure of the Western intelligence community to read Putin’s mind. Indeed, the underlying principle of successful deterrence is that the deterrent signal must penetrate the adversary’s filters of history, culture, language, religious and ideological axioms, and social-psychological factors. On the practical level, it must also penetrate the filters that shield an autocratic leader from bad news and from information that contradicts his thinking. The history of deterrence is replete with examples of deterrent messages and warnings that were not received as intended. This was the case with Saddam Hussein, whose closest advisors did not dare tell him that the US was almost certainly about to invade. This also seems to have led Putin to underestimate the resistance his invasion would encounter in Ukraine.

But successfully delivering a deterrent threat to an adversary’s leadership is not enough. The threat must also be credible. And for a threat to be credible, it must be backed by a record of carrying out comparable threats. The adversary must be confident that the projected consequences of his proposed action will heavily outweigh any benefit he may achieve by carrying it out. However, cost-benefit analyses are subjective. The consequences must threaten things valued by the deterree, which may not be a mirror image of things valued by the deterrer. What’s good for the goose is not always good for the gander. A doctrine of “tailored deterrence” must therefore take into account the psyche of an adversary’s leadership, identification of the decision-makers with the interests which are threatened, and the dynamics of threat assessment within that leadership.

The debate over tailored deterrence dates back to the early days of the Cold War, when deterrence was perceived, by and large, as a “one size fits all” doctrine based on a rational-actor model. As such, it ignored cultural and religious factors that have a potentially far-reaching influence on the susceptibility of an adversary’s leadership to deterrence. In his 2001 monograph, The Fallacies of Cold War Deterrence and a New Direction, Keith B. Payne points out that the narrative favored by analysts immediately after the Cuban Missile Crisis is now anachronistic. It was developed before the two superpowers had built the stockpiles and delivery systems for mutually assured destruction, and the command-and-control mechanisms required to prevent such a catastrophe. It also ignores the evolution of the relationship between these factors and the cases in which they took the world to the brink of nuclear war.

How softly to speak and how big a stick?

US president Theodore Roosevelt was fond of the adage, “Speak softly and carry a big stick.” In a letter to the US Ambassador to Britain, Whitelaw Reid, in December 1908, he wrote: “I want to make it evident to every foreign nation that I intend to do justice; and neither to wrong them nor to hurt their self-respect; but that on the other hand, I am both entirely ready and entirely able to see that our rights are maintained in their turn.” Roosevelt’s “big stick” doctrine rested on five principles:

1. Possess a robust military capability that would force the adversary to pay close attention.
2. Strike only when prepared to strike hard.
3. Never bluff.
4. Cultivate an image of fairness to nations that do not act against American interests.
5. Allow the adversary to save face in defeat.

The first three principles comprise the essence of conventional deterrence. Roosevelt believed that a big stick was not sufficient to guarantee deterrence. Adversaries must be persuaded that the stick’s owner was willing to use it without reservation should the need arise. This is the essence of credibility. If the owner of a big stick is caught bluffing, the stick loses its potency as a deterrent. The validity of this reasoning has not diminished since it was formulated at the turn of the 20th century.

The credibility of a threat is not objective, it depends on perception. And this perception is based on a history of past behavior over time and in a variety of cases. It is not enough to simply “speak softly and carry a big stick”—it is necessary to demonstrate, even on a lesser scale, a willingness to actually use the stick. Recent US policy in the Middle East and Afghanistan has demonstrated precisely the opposite. Putin was therefore able to conclude with some confidence that NATO would not react with military force to the unprovoked pulverization of a neighboring country.

The other necessary condition for effective deterrence is that the nature of a party’s response must be commensurate with the threat posed by his adversary. This comprises three factors: the domain of the response (economic, political, conventional military, or nuclear), its scale (single act of retaliation, continuous and possible escalating pressure, the threat to escalate from one domain to another), and its goal (to punish the aggressor and force him to withdraw, to topple his regime, or even to destroy his entire country).

For deterrence to be effective, the domain of the response must correspond to or exceed the domain of the threat by the adversary. No amount of speaking softly can compensate for the absence of the big stick. Rarely can a military threat be countered by a threat which does not include a corresponding military component.

The scale of the retaliation relates to the nature of its targets. This brings us back to tailored deterrence, and the distinction between “counter-force” and “counter-value” retaliation—the former relates to attacks on military targets, and the latter to attacks on an adversary’s economy and population. For a target to be deemed a “counter-value” target, it must have value in the eyes of the deterree that is comparable to the target of the deterrer that it threatens. Indeed, in his question to Kennedy, Charles de Gaulle made a “counter-value” comparison of Paris to New York (not Paris to Washington, DC).

However, the public mood in the US—and consequently that of consecutive administrations—is strongly against punishing an enemy population for the iniquities of its (autocratic or unelected) leadership. This is well known to the Kremlin, and significantly erodes any deterrence based on “counter-value.” In 2018, I participated in an exercise with US academics from leading universities. The scenario was an imminent threat by North Korea to a city in the US. The near consensus of the participants was that even if there was near certain intelligence on such an impending attack, there was no justification to execute a pre-emptive nuclear attack on North Korea that would cause the death of innocent civilians who were not a party to their government’s actions. Even in a scenario of an actual attack and “counter-value” retaliation, the consensus did not change much.

Nor can the scale of threatened retaliation remain constant—it must keep pace with an adversary’s escalation. The cost of yielding to deterrence before a military aggression may be to accept that certain national goals must be postponed (but not necessarily renounced). However, if deterrent messages are ignored and an adversary proceeds with an attack, the price of submitting to compellence (by, for example, withdrawing from territory) rises—defeat in Afghanistan precipitated the collapse of the Soviet Union, and defeat in the Falklands War led to the fall of the Argentinian regime. The intensity of the threat needed to achieve compellence must, therefore, also rise.

This is certainly the case for the prospects of effectively compelling Russia to withdraw from Ukraine. As the war drags on, the fate of Russia—and of Putin personally—becomes more closely tied to its outcome. Putin has more to lose by concessions and compromise than he did before he launched the invasion, and so the intensity of the threat required to force him to make those concessions must go up.

Finally, the goal of the retaliation must be commensurate with the threat. Despite Israel’s official policy of “nuclear ambiguity,” Israeli leaders—including late President Shimon Peres who is credited with building Israel’s nuclear deterrent—have warned Iran that if it were to attack Israel with a nuclear weapon, it too could be “wiped off the map” and “sent back to the stone age.” This is a clear threat by a formally “non-nuclear” state to wreak the kind of destruction on an enemy that can only be achieved with nuclear weapons (a possible allusion to EMP). No NATO deterrence statements have ever included such warnings.

Looking forward

The degradation of American deterrence has many ramifications. Beyond the immediate aim of restoring Ukraine to Russia, the goal of Putin’s invasion is the “re-imperialization” of Russia. This concept was introduced by Henry Kissinger in 1994, in reference to the potential threat to the West posed by Moscow’s intention to preserve its zones of influence in the post-Soviet space. The right of Russia to defend what Yeltsin called its “compatriots abroad” in the former Soviet republics is the key element of this process. (Russian federal law defines the term “compatriot” in a capacious manner, enabling the Kremlin to consider virtually anyone with ties to Russia or the former Soviet Union as a “compatriot.”)

Putin hopes to revive Russia’s image as a “Great Power,” and to persuade public opinion in the West and in the former Soviet-bloc countries that the West, NATO, and the US are paper tigers. In a way, the latter aim has already been achieved. The secondary victim of the Russian invasion—after Ukraine—is, therefore, the perception of Western deterrence in the eyes of the countries which dare to rely upon it for their survival as independent states.

The most immediate repercussions will be felt by the NATO countries bordering Ukraine. The scenario of a protracted Russian occupation and Ukrainian resistance will create constant tension between these countries and Russia, and an ever-present risk of Russian cross-border retaliation or covert action (assassinations, bombings) against Ukrainians in those countries. Russia will also continue to issue military threats towards erstwhile Soviet satellites (Czechia, Slovakia, Poland, the Baltic states) which are now members of NATO. If NATO does not pose a credible military deterrent to these provocations, its deterrence will erode further. The former Soviet satellites are likely to form a sub-alliance within NATO or even a separate alliance in order to bolster their own defenses.

Another long-term consequence of the failure of Western deterrence in Ukraine is the possibility of a new age of nuclear proliferation. Strategic thinkers in countries that currently enjoy US extended assurances point out that if Ukraine had not surrendered the nuclear arsenal it inherited when the Soviet Union dissolved, it would have been a lot less vulnerable to invasion by Russia. Countries which have dabbled with the idea of acquiring nuclear weapons and suspended such ambitions—Saudi Arabia, Egypt, and Turkey in the Middle East, and Japan, Taiwan, and South Korea in Eastern Asia—may now be rethinking their position.

However, in such a poly-nuclear world, safeguards—levels of command-and-control, permissive action link systems, intelligence to verify that states are reacting to reality not disinformation, separation of weapons and delivery systems, and the absence of second-strike capabilities—will be far less effective than those which stabilized the original Cold War. This will make deterrence more difficult. To predicate a strategy on a belief that nuclear weapons impose an enhanced sense of responsibility on their possessor that reduces the risk of conflict (as Kenneth Waltz contended in 1981) would be a perilous gamble. Command-and-control of nuclear weapons in different countries is highly influenced by the nature of the regime, its centralism, the accountability of leaders (democratic or autocratic), culture, religion, and levels of trust of the leadership in the military. Multiple nuclear actors will make deterrence tailored to each and every one of them difficult.

In addition to the failure of deterrence, NATO has not been able to achieve escalation dominance during the Ukraine crisis. The lack of a robust response to the Russian elevation of its nuclear alert is a signal to all: not only did NATO fail to prevent the introduction of a nuclear component into a conventional crisis, but that component was introduced by only one side. This will have long-term effects on the perception of NATO assurances by friends and foes alike.

The only positive is that China is highly unlikely to be encouraged to act against Taiwan. Beijing realizes that Taiwan—unlike Ukraine—has significant economic and strategic value for the US and its Asian allies, Japan, South Korea, and Singapore. Taiwan is also a highly developed country with an advanced military, which Ukraine is not. The Chinese desire to reabsorb Taiwan is a broad national objective, but it is not the personal obsession of a particular leader who yearns to achieve it in his lifetime. The Chinese can wait and certainly have no interest in inviting the kind of economic punishment and international pariahship to which Russia is now subject.

The future of US nuclear deterrence

So, where does that leave the issue of US nuclear deterrence? The paradigm before Hiroshima was that reputational perceptions are created by actions and amplified by hearsay, and that declarations are only as valid as the memory of past conduct. “Deterrence by example” prevented the need to use greater force. Conversely, a bluff called in one instance, whatever the pragmatic justification, necessarily diminishes the credibility of future threats.

This paradigm could not apply in the world of nuclear weapons, because their destructive power made deterrence by example impossible. The Cold War was therefore a standoff between two rational superpowers, neither of which was driven by eschatological fervor. Each had the capacity to destroy the world, a second-strike capability, reasonably good intelligence on its adversary, and strong command-and-control paradigms. In a “poly-nuclear” world, these factors will not exist at the same level in all the new nuclear powers. As I have previously argued elsewhere, this is certainly true in regards to countries in the Middle East. The chances of initiating a nuclear strike based on erroneous intelligence, miscalculation, or the absence of a “second strike” capability will grow.

This raises the question of whether the paradigm of conventional deterrence should be uncoupled from the nuclear paradigm to allow for a more proactive deterrence by example. The US fear of engaging a nuclear adversary in a conventional conflict—even by providing military support to an attacked country—severely restricts NATO’s courses of action in response to any conventional threat. Despite the sanctions, the lesson Russia will learn from the Ukraine crisis will be that Russia can attack another country without worrying about international military reprisal.

In his 1962 book, Thinking About the Unthinkable, Herman Kahn proposed that a policy of nuclear response must “look and be both prudent and rational.” In Arms and Influence, published four years later, Thomas Schelling pointed out that “Soviet expectations about the behavior of the United States are one of the most valuable assets we possess in world affairs.” Putin certainly seems to have believed President Biden when he declared that the US would not become involved in fighting Russia in Ukraine. But this will not necessarily be the case when faced with a fanatical adversary who refuses to believe anything he hears from an American administration. The potential for conspiracy-theory-driven leaders with nuclear weapons to resist de-escalatory messaging will be a persistently destabilizing element.

One alternative to a “prudent and rational” approach that cultivates the adversary’s expectations about US behavior is the concept put forward by the Israeli strategic thinker, Yehezkel Dror. Dror proposes to base deterrence on the image of a “crazy state”—one that may actually use nuclear weapons in a pre-emptive attack—thereby reinforcing the perception of a willingness to use its nuclear capability. However, as noted above, this is a difficult strategy to implement in democratic societies that have developed robust norms against military aggression.

A preferable strategy may be ambiguity regarding the thresholds that precipitate the use of nuclear weapons. This is a dangerous area, and such a posture must take into account the corresponding posture of the adversary. A country like Iran that views nuclear weapons not only as a deterrent, but also as a means of pursuing regional hegemony, will be more likely to integrate this capability in its day to day strategic posture. The example of the Ukraine crisis, in which the US/NATO refused to be baited by Russia’s announcement of its new nuclear alert status, is likely to be counter-productive against such an adversary. The satisfaction such an adversary would get from successfully challenging the US with impunity is likely to lead to further escalation.

As a matter of policy, the US and NATO must decide what level of saber-rattling should be deemed sufficient to warrant a reciprocal nuclear alert. Although a reluctance to engage in—or even threaten—military action has contributed to the Long Peace enjoyed by the democratic world since the end of the Second World War, it has also made the undemocratic world more dangerous. Belligerent autocrats like Putin, unrestrained by such Western taboos, have been encouraged to believe that they can pursue their imperial ambitions with impunity. The invasion of Ukraine has provided risk-averse Western publics and politicians with a reminder that the best way to avoid military conflict is, paradoxically, to threaten force and commit to using it where necessary. If we are to achieve a more peaceful world, the West needs to rediscover the meaning and importance of credible deterrence.