Air Force airmen load cargo on a C-17 bound for Poland at Pope Army Airfield, N.C., Feb. 10, 2022.

Air Force airmen load cargo on a C-17 bound for Poland at Pope Army Airfield, N.C., Feb. 10, 2022. James Bove, Air Force

How to Gauge the Risk of a Nuclear Escalation with Russia

Escalation theories can help NATO policymakers avoid nuclear war—but it is ultimately up to Putin.

As Russia’s Vladimir Putin continues to direct his military to commit war crimes and officials threaten the use of chemical weapons in Ukraine, the West’s angst over crossing a notional red line that would spark an escalation toward nuclear war has complicated the calculus over which weapons deliveries are more dangerous than others. These concerns are justified based on Russia’s irresponsible rhetoric, but some claims about an inevitable escalation lack academic rigor. 

Luckily, escalation theory is an academic discipline that can help policymakers gauge the risks of the next proposed package of U.S. military aid to Ukraine. As it happens, escalation theories provide much more flexibility for aggressive U.S. actions in Ukraine than many realize. But there is a limit, as these theories also explain how nuclear escalation could become inevitable, even if the United States contributes nothing more to Ukraine’s defense. 

The situation in Ukraine just a few weeks ago—in which Russia’s advances seemed to have stalled—seemed to indicate that the decision by Western powers to provide Ukrainians only material support initially was prudent. Since then, however, Russia has redirected and concentrated its military’s attention and firepower on a new objective: seizing the Donbas region in Ukraine’s east. In response, the United States and NATO took more aggressive steps and authorized heavier firepower, such as howitzer artillery guns, new armed drones, and additional attack helicopters. But NATO leaders continue to reject Ukrainian President Volodymyr Zelenskyy’s requests for stronger measures like imposing a no-fly zone, sending advanced weapons like fighter jets, or even directing NATO-member attacks on Russian military targets—at least for now

If the U.S. or NATO decides to take a stronger stance, examining the conflict through a combination of escalation theories can provide a clearer picture of the risks associated with fighting even someone as unpredictable as Putin. 

Take those who want to escalate. No-fly zone supporters like Rep. Adam Kinzinger, R-Ill., have argued that ethics demand a more robust U.S. response. Others, like National Interest editor Jacob Heilbrunn, say a strong stance in Ukraine is necessary to stymie Putin’s more ominous goals. This rhetoric might seem inflammatory, but some Cold War-era theorists would be perfectly comfortable with it, as enacting those measures would not necessarily lead Russia and NATO into nuclear war. 

Herman Kahn’s escalation ladder is probably the most-quoted theory regarding nuclear conflict, and at first glance, Kahn’s ladder does imply that conventional conflicts could act as precursors to nuclear war. However, in Kahn’s theory, actors do not necessarily move sequentially or steadily towards escalation; conventional warfare or even limited nuclear strikes might just as likely lead to de-escalation in specific scenarios. 

In other words, Kahn’s ladder does not imply inevitability, and the mechanisms that might push a country towards the nuclear threshold are convoluted and difficult to quantify. Instead, an applicable concept of Kahn’s 44-step ladder differentiates between when nuclear war is “unthinkable” and when a conflict has crossed the threshold into “potential nuclear use.” The ninth rung of Kahn’s ladder, under which a no-fly zone would fall, is “dramatic military confrontations” but it is still under the threshold of nuclear use becoming thinkable. Rationally, there is no certainty of a nuclear confrontation at this rung because the horrors and potentially suicidal risks of nuclear war during a conventional fight are just as real as in peacetime. 

Those who argue against a no-fly zone over Ukraine could also justifiably point out that the ninth rung is the last step before Kahn theorizes that nuclear war becomes distinctly possible, a threshold obviously worth avoiding. Yet, ten more rungs on Kahn’s ladder still exist before an actor escalates to nuclear use. So, what specifically would cause Putin to escalate one more rung, into the “thinkable,” or bypass significant conventional conflicts and move up ten rungs directly to a limited nuclear war? Would it be a no-fly zone?

According to theorist Robert Powell, probably not. Powell cites Snyder and Diesing’s “crisis equilibrium” concept in building limited nuclear war models, stating that there is “no crisis equilibrium unless one state challenges another and this challenge is resisted.” In Ukraine, a clearly articulated no-fly zone or similar effort is a challenge to Putin, but notably not a nuclear challenge. It does not have to start Powell’s version of nuclear escalation. Many misunderstand this pivotal point in the conversation around no-fly zones or increased lethal aid and nuclear escalation: for a no-fly zone to be escalatory, it must push Putin into a crisis equilibrium. 

This might sound promising, but the sinister side of Powell’s model is that entering the crisis equilibrium is less about the opponent’s actions and more the mindset of the instigator. By that logic, simply losing the war irrespective of NATO aid could push Putin to escalate. It is not NATO involvement that increases the probabilities of nuclear use; it is how Putin responds to losing the war. Should Russia fail or even be driven out of Ukraine, Putin will blame NATO and the United States for supplying Ukraine with weaponry. He might act just as he would if it were NATO jets shooting down Russians instead of Ukrainians with NATO-supplied surface-to-air missiles. Even if NATO withdrew its support from Ukraine entirely, Putin could enter a crisis equilibrium if his invasion crumbles.  

Still, in the unlikely scenario of Russian and U.S. forces fighting in direct combat, rules governing nuclear escalation apply. Using nuclear weapons is not inherently any more beneficial for Putin just because he is losing a limited conventional fight. It introduces a new set of risks, according to Powell’s theory. If Putin is not confident that using nuclear weapons will cause Ukraine (and NATO) to accept defeat, he will have gained nothing by starting the “game.” Therefore, implementing a no-fly zone against Putin’s forces has no impact on escalation if he is a rational actor and his grip on power is secure. Indeed, implementing a non-nuclear measure like a no-fly zone might even play into Putin’s propaganda and open an avenue for him to accept a de-escalation, remain legitimate, and find a compromise (as Thomas Schelling described and the Atlantic’s Tom Nichols chillingly explains here). 

On the other hand, Kahn also describes in his work how one side in a conflict might escalate if they believed the other side could or would not match them. Putin might see value in “trying to scramble the deck with escalatory threats” if U.S. and NATO resolve weakens. To block him, U.S. and NATO leaders could assert that using a nuclear weapon would be met with a nuclear response. Still, that threat would only be as good as Putin’s belief in it, and if he found himself losing a conventional fight, he still might hope to scare away NATO with a limited nuclear strike. 

Frustratingly then, the theories of Kahn, Schelling, and Powell alone do not give policymakers enough to assess risk. If Putin might use a nuclear weapon no matter what the United States and NATO do, what is the logic in not aggressively intervening to stop the ongoing war crimes in Ukraine? 

“No one really knows what the probability is that things will go wrong. In particular, no one could put together a completely persuasive story to a hostile and skeptical audience,” Kahn warned. Putin already invaded Ukraine under questionable circumstances and despite ominous warnings from senior Western leaders. Kahn would likely scoff at the idea of Putin leaping to a nuclear conflict over a limited no-fly zone, but he also acknowledged the inherent risks between nuclear-armed adversaries. 

James Acton of the Carnegie Endowment expanded on this concept with a helpful framework describing escalation in Ukraine as sets of probabilities and risks. The rational probability that Putin would escalate without U.S. involvement is low, but the risk of a nuclear conflict is exceptionally high. However, probabilities increase with the enforcement of a no-fly zone, not because it is directly escalatory as Kahn shows, but because of the inherent opportunities for unintended escalation – the risk remains constant. 

The increased probabilities of nuclear escalation due to unintended threats are what should give the U.S. and NATO pause, as any number of circumstances might make Putin think his regime is at risk. Policymakers would face a whole new set of potential questions: What if a cruise missile is mistaken for a nuclear weapon? Or a lightning-quick U.S. victory convinces Putin that the real goal is regime change in Moscow? What if Putin finds himself choosing between an embarrassing loss or a perceived escalate-to-de-escalate opportunity? 

Unless the effort is perfectly focused and communicated, the United States could be increasing the probability of unintended escalation by entering the conflict even in a limited capacity. Policymakers should also understand and communicate publicly that while supplying Ukraine with some weapons might increase the odds of Putin losing and resorting to nuclear use, those efforts are no direct threat to Russia or Putin—they are a limited response to a limited conflict that NATO did not initiate. A no-fly zone, however, is still probably not strategically sound given the potential for unintended escalation and the current order of battle in Ukraine. 

One final—and somewhat obscure—theory provides the opportunity to examine the risk of increased allied intervention in Ukraine should it become necessary. “Regime insecurity theory” generally states that authoritarian foreign actions are driven by their desire to remain in power. Regimes might implement conflicts to enhance their own legitimacy or eliminate highly visible counter-narratives to their grip on power (the exact reason Putin invaded, arguably). However, researchers have also found that authoritarians are more likely to de-escalate if they can obtain assurances to maintain power (in Putin’s case, relief of sanctions and something to claim victory over, like “liberating the Donbas”). 

Ultimately, the most dangerous course of action becomes most likely if Putin perceives that starting a nuclear conflict will keep him in power. It is not a comforting solution, but after examining the theories of Powell, Kahn, and others, the real key to preventing Putin from using a nuclear weapon lies in making it readily apparent that the United States and NATO are no threat to Putin’s regime, regardless of whether they intervene conventionally. Increasing lethal aid is probably less risky than some fear, and while direct conflict is certainly not advisable at this time, theory provides that it need not escalate to nuclear war.

Maj. Shane Praiswater, Ph.D., is a former military analyst at the Center on Military and Political Power at the Foundation for Defense of Democracies and a fellow at Johns Hopkins’ School of Advanced International Studies. Views expressed or implied in this commentary are solely those of the author and do not necessarily represent the views of the U.S. Air Force, the Defense Department, or any other government agency.