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In recent weeks, multiple Western countries have authorized Ukraine’s use of imported weapons for strikes on Russian territory, crossing one of the Kremlin’s many rhetorical “red lines.” Thus far, the Russian response has also been entirely rhetorical, with Vladimir Putin threatening to supply weapons to Moscow’s international partners for use in potential strikes against “sensitive facilities” of Ukraine's allies around the globe. From the very start of Russia’s full-scale invasion of Ukraine, Putin and members of his regime have attempted to use nuclear blackmail to limit Western support for Ukraine. Little by little, however, the Western world has been exposing the Kremlin’s so-far empty rhetoric. Only two years ago, the West was hesitant to transfer even obsolete tanks to Ukraine. Now NATO countries are openly exploring the possibility of sending contingents of military instructors.

  • The red lines of the Ukraine war

  • How Ukraine and NATO tested Russia’s red lines

  • Red lines and military strategies


The red lines of the Ukraine war

The war in Ukraine is the largest conflict in Europe since World War II, with military killed and wounded topping 500,000, the number of refugees exceeding 6 million, economic damage approaching an estimated $500 billion, and tens of thousands of civilians falling victim to Russia's constant violations of the rules of war. However, considering the fact that the aggressor country possesses nuclear weapons and has been threatening to use them from the onset of the conflict, the casualty count could be many times greater if the war truly were to spiral out of control. As a consequence, Kyiv's allies have chosen to tread lightly, trying to protect Ukraine on the one hand while preventing nuclear escalation on the other. One of Moscow’s main instruments of deterrence is the use of so-called “red lines” — verbal statements purportedly indicating which Western actions decision-makers in the Kremlin deem to be intolerable.

One of the main instruments of deterrence in armed conflicts is so-called red lines

Putin declared his red lines at the very beginning of the war, announcing on Feb. 24, 2022:

“Whoever tries to interfere with us, or worse, to threaten our country and our people, should know that Russia's response will be immediate and will bring about consequences that you have never faced before in your history.”

His rhetoric was difficult to misinterpret: the Russian president was saying that if Western countries entered the war on the Ukrainian side, Russia was prepared to respond with nuclear weapons. But although Putin declared from the outset his readiness for the highest possible escalation, he did not define what he considered to be a “threat to the country,” reserving the right to judge in each individual case whether the purported red line had been crossed.

Vladimir Putin delivers an address on the launch of Russia's “special military operation,” Feb. 24, 2022
Vladimir Putin delivers an address on the launch of Russia's “special military operation,” Feb. 24, 2022

The West has adopted a different approach. While no public statements have been made about what the reaction to Russian nuclear use might be, Polish Minister of Foreign Affairs Radoslaw Sikorski recently said that the Kremlin had received a signal: if Russia were to use nuclear weapons in Ukraine or to attack a NATO country using conventional means, all Russian military infrastructure would be destroyed using conventional (that is, non-nuclear) means. American war games conducted in the years before Russia’s full-scale invasion suggest that such a Western response to Russian nuclear use has been well thought through. By using conventional weapons to respond to a nuclear attack, NATO would be able to demonstrate its resolve while retaining the potential to escalate further in the event that the Russian side launched a second nuclear strike. Such a nuanced approach makes NATO’s threatened response much more credible, as it is entirely plausible that the West is prepared to strike Russian military infrastructure with conventional weapons, counting on the Kremlin not daring to respond with an all-out nuclear attack lest it result in a retaliatory nuclear strike on Russia.

But drawing lines is only the first step. The hard part is convincing your opponent you are ready to carry out the threat. This is where the sides have chosen different strategies. Putin wanted the West to perceive him as a man who had little regard for the costs and was ready to die in a nuclear war if he had to, destroying the whole country along with him. He borrowed this strategy from the Democratic People’s Republic of Korea — the northern one — whose leaders have been successfully exploiting such a strategy for decades while doing little more than occasionally launching ballistic missiles on holidays. Creating a believable madman image was not a difficult task for Putin, as nuclear threats have been a constant in his speeches — and in Kremlin-controlled propagandist talk shows — for years. Russia's strengthening military dictatorship has left no doubt that the president, as the supreme commander-in-chief, is its sole decision-maker, and Putin's interviews, which feature lengthy lectures on “alternative history” and suggestions that Russians are ready to sacrifice themselves and “go to paradise like martyrs,” have made it clear that counting on the Russian leader’s sanity would be too risky.

Putin has borrowed North Korea's nuclear blackmail strategy

The rhetoric and behavior of Western leaders are more constrained, as their voters may not be interested in the prospect of making a nuclear sacrifice for the sake of some supposed greater good. As a result, Ukraine and NATO countries have chosen a different tactic, known in conflict studies as “salami slicing” (which was made famous by the dark comedy “Dr. Strangelove,” a film Putin is known to have watched). The essence of the strategy is to escalate the situation progressively, in small steps, acting on the assumption that the enemy will not initiate a full-scale nuclear clash as the direct result of any individual step. NATO’s response to the Russian invasion of Ukraine offers a case study.

How Ukraine and NATO tested Russia’s red lines

The Russian invasion plan of Feb. 24, 2022, relied on the assumption that special operations forces would quickly succeed in capturing or eliminating the Ukrainian government, that Ukrainian military and volunteer forces would not put up significant resistance to Russia proclaiming its proxies as the legitimate rulers in Kyiv, and that Russian troops would therefore be able to take control of the country without a fight — and to do so before the West was even able to coordinate a response. However, after the Russian airborne landing at Hostomel airport failed, Russian troops elsewhere in Ukraine found themselves in a fierce battle with a Ukrainian military whose partners in Washington had widely shared the intercepted Russian invasion plan months in advance. Still, Russia’s numerical advantage was so enormous that it was clear Ukraine would not last long without material assistance from its Western allies, who in addition to fears of “escalation” worried that any high-tech systems sent to Ukraine might eventually end up being captured by Russian forces.

Fighting in the Hostomel area, early March 2022
Fighting in the Hostomel area, early March 2022
The Main Intelligence Directorate of the Ministry of Defense of Ukraine

Despite Western shipments of man-portable anti-tank and anti-aircraft weapons in the month leading up to the Russian invasion, the first weeks of the full-scale war saw Ukraine make do largely with its own willpower and resources — an effort aided to no small extent by the catastrophic ineptitude its Russian adversary demonstrated when suddenly faced with the prospect of a real war. This stage turned out to be crucial for the Western allies: contrary to the worst-case scenarios presented by their intelligence services, Ukraine’s regular military had proven capable of sustaining the fight without turning solely to the use of guerilla tactics. Suddenly, the provision of larger, more sophisticated military support warranted a serious discussion.

At first, military assistance was minimal. On Feb. 27, 2022, Germany signed off on the delivery of nine howitzers from Estonia, and the United States transferred 200 more Stinger man-portable air defense systems within the framework of previously approved assistance. On Feb. 28, Poland transferred 100 mortars with ammunition and began discussing the transfer of several of its fighter and attack aircraft to Ukraine. France sent arms worth €120 million, including Milan and Javelin anti-tank systems and Mistral MANPADS. Many other countries sent similar weapons: grenade launchers, mortars, MANPADS, shells, and body armor. All of this was certainly useful but could not turn the tide of hostilities.

Only in late March 2022, when it became clear that Russian troops had failed to take Kyiv and the AFU had launched a counteroffensive, did the Western allies ramp up their support. In April 2022, Ukraine started receiving heavy artillery, armored personnel carriers, and Czech T-72M1 tanks. The U.S. finally declared its readiness to supply HIMARS multiple rocket launchers, although the first modest batch of just four HIMARS would not reach Ukraine until June of that year. German tank manufacturer Leopard also volunteered to start deliveries to Ukraine, but the German government did not dare to cross this red line at that time.

An American HIMARS system handed over to the AFU
An American HIMARS system handed over to the AFU

Similarly, the Western countries did not dare to introduce a “no-fly zone” over Ukraine, as that would have required NATO forces to involve themselves directly in the war by shooting down Russian aircraft over Ukrainian territory. However, the effectiveness of Ukrainian air defense largely resolved the issue, and Russian jets have mostly stopped flying deep into Ukrainian territory due to the risk of being shot down by Ukrainian defenses.

As Ukraine demonstrated its capacity to plan and conduct large-scale counteroffensive operations, the flow of Western weapons only increased. In the fall of 2022, Germany transferred its multiple rocket launchers to Ukraine; the U.S. sent more HIMARS, more howitzers, and 1,000 more Javelin anti-tank systems; and several European countries followed suit with artillery systems and armored vehicles. One by one, nearly all Western countries eventually joined the military assistance effort. Seeing that none of their peers had suffered any catastrophic consequences, they grew increasingly bold in supplying Ukraine with state-of-the-art weapons.

In October 2022, the Ukrainians tested a new red line, partially blowing up the Kerch Bridge, the only road connecting occupied Crimea to mainland Russia and a prestige project near and dear to Putin’s heart. Once again, Russia did nothing, and the entire peninsula has now become a constant target of Ukrainian attacks. Whereas before the full-scale invasion no one thought Ukraine might try to regain control of the peninsula by force, in the run-up to Ukraine’s counteroffensive of 2023 such plans were under serious consideration. By May 2023, the red line drawn in 2022 had shifted to Russia's internationally recognized borders, making Crimea and Donbas accepted targets for the Armed Forces of Ukraine.

In 2023, the allies tested more red lines. February saw Germany agree to provide Ukraine with Leopard tanks, which served as a symbol of Germany’s full commitment to its obligations to Ukraine, even if the Leopards proved incapable of providing a decisive advantage on the battlefield. In May 2023, Ukraine delivered its first blow to Moscow directly, when several drones crashed into the Kremlin itself. Although the Ukrainian UAVs did not cause any serious damage, the psychological effect was tremendous: for the first time in the war, residents of the Russian capital realized that they, too, could find themselves trapped in a war zone. Later, drone raids on Moscow would become a regular occurrence, and the damage from their strikes would cease to be purely symbolic. Putin struggled to find an adequate response to this escalation, as Russian missiles had been hitting Ukraine's residential areas since day one of the full-scale invasion. When faced with strikes on the Russian homeland, there was simply nothing in the Kremlin's arsenal Putin could turn to as a means of escalation — except, of course, to nuclear weapons.

The Insider

Observing these developments, Ukraine's Western partners yielded to the pressure of public opinion and in August 2023 agreed to supply Ukraine with F-16 fighters (understanding that it would still take months to train Ukrainian pilots to use them). Moreover, last September, Russian troops could feel the enemy crossing another important red line, as Ukraine began the systematic use of long-range cruise missiles. At first, they targeted Crimea, with the first British Storm Shadow hitting its mark last September. In October, Ukraine received ATACMS missiles. After that, Crimea lost its former strategic significance, as all Russian military facilities on the peninsula became easy targets. Russia was compelled to move its Black Sea Fleet from Sevastopol to the southern port of Novorossiysk to keep it safe from the naval drones developed by Ukraine.

The transfer of long-range missiles came so late precisely because, in the first year of the war, Western countries feared that strikes on Crimea could lead to an uncontrollable escalation of the conflict. Once this taboo was broken, Ukraine's Western allies maintained only the last red line, refusing to allow the use of their missiles for strikes against internationally recognized Russian territory. Ukraine had long been carrying out sabotage missions inside Russia, attacking oil refineries and blowing up military warehouses with drones (again, Russia did nothing in response). Still, the West refused to approve of Ukraine responding with direct missile strikes, even though Russia had been launching missile strikes against Ukrainian military and civilian targets over the entire course of the full-scale war. Who knows how long this self-imposed Western red line would have lasted had Putin not come up with the idea of creating a “sanitary zone” near the Russian border in Ukraine’s Kharkiv Oblast? After Russian troops launched an offensive from their territory, taking advantage of Ukraine's inability to hit rear areas with high-precision Western weapons, the Western ban was finally lifted.

In the first year of the war, the West feared that strikes on Crimea could lead to an uncontrollable escalation of the conflict

This leaves the last of Putin's red lines: the deployment of active-duty NATO troops to Ukraine.NATO instructors have, of course, trained Ukrainian troops on the territory of NATO countries, but now French President Emmanuel Macron appears to be seriously exploring the possibility that trainers could be sent to Ukraine itself. Even if they do not take part in hostilities, the presence of NATO troops in Ukraine could drastically boost the AFU’s combat effectiveness. This red line also has a symbolic importance, precisely because it is the last one before the full participation of NATO armies in the war becomes a real possibility.

Red lines and military strategies

According to some analysts, Putin made a strategic mistake when, at the start of the invasion, he immediately and publicly labeled Western involvement in the conflict a red line beyond which catastrophic consequences were inevitable. Politicians in general try not to publicly mark red lines, notes Branislav L. Slantchev, professor at the University of California, San Diego, and a specialist in military coercion, intrawar negotiations, and game theory analysis of war.

“First, the state declaring the red lines does not want to be in a position where it would be forced to respond just because the red line was crossed. It always wants to retain freedom of action to decide on the best course under the circumstances. Second, you do not want to corner the opponent. By making public declarations, them not crossing the line can be attributed to the declaration, and so is seen as a weakness. This might give the opponent extra incentive to cross it just to avoid that inference. This is a situation that neither side would want. That’s why real red lines are communicated privately.”

As Nobel laureate Thomas Schelling noted in his classic work “The Strategy of Conflict,” for the enemy to believe that your threat is real, they must see that you have already cut off your escape routes and are bound by the necessity of carrying it out, even if you harm yourself in the process. For example, by accelerating hard in a car, you cause those moving in the opposite direction to swerve because they realize you can't stop. This may have been Putin's gamble when he publicly announced his plan to take over all of Ukraine, cutting off his path to any intermediate solutions and thereby making it useless for the West to pressure him. His threat sounded even more credible considering that, as a dictator, Putin could afford to ignore the potential costs of risking hundreds of thousands of lives of his fellow citizens.

Putin's gamble could have paid off had he managed to seize Ukraine in the first days of the full-scale war, but as the fighting dragged on, several problems arose at once. First, the horrors of the unfolding humanitarian catastrophe awakened the Western general public, which demanded that their leaders intervene. Second, the Western allies had plenty of time to coordinate and start acting together. This poses a huge challenge for Putin: he can attempt to intimidate one, maybe a handful of countries, but no one will believe that he can take on the entire world, as he simply does not possess the resources to do so.

Consequently, as soon as one country tests yet another red line, other allies immediately muster up the courage to follow suit. As Slanchev notes:

“Most countries would not be the first to supply advanced weapons systems. Germany is a good example of this – they wait for the U.S. to take the lead, just like we did with the tanks, symbolic as that lead was. Others, like the UK and the Netherlands, try to prod the U.S. into doing more by taking the first step themselves, hoping that this would make it easier politically for the U.S. to do it.”

Every single step taken by the West changes the status quo so slightly that it deprives Putin of the political justification for nuclear war, and thus, in full accordance with the “salami-slicing strategy,” the allies are crossing Russia’s red lines one by one. Importantly, Western allies take some of the steps only as retaliatory measures. For instance, deliveries of the first long-range versions of ATACMS were agreed upon only after the Kremlin ignored the warning not to use North Korean ballistic missiles on Ukrainian territory, and missile strikes on Russian territory were not authorized until Russia launched its shelling offensive on Kharkiv Oblast.

Employing the “salami-slicing strategy,” the allies are overcoming Putin's red lines one by one

Realizing that the West is paralyzed by the fear of nuclear war, Kyiv is doing all it can to prove that Putin's threats are a bluff. It could have been to that end that Ukrainian drones recently attacked several facilities related to the combat control system of Russia’s strategic nuclear forces (SNF):

  • The receiving part of the 29B6 Konteyner (Container) over-the-horizon radar station in Mordovia
  • The Voronezh-DM over-the-horizon radar in Armavir
  • The Voronezh-M over-the-horizon radar near Orsk.

All of the above facilities are part of Russia’s early warning system, SPRN — one of the key elements of its Strategic Nuclear Forces. Each of these attacks formally fits the criteria for retaliatory use of nuclear weapons by Russia. The U.S. administration has expressed concern about Ukraine's attempts to damage Russian SPRN stations, which play no role in the Ukraine war. However, these attacks have had a psychological effect: if Russia does not react to strikes on nuclear facilities, there is no need to fear that strikes on military airfields in the Belgorod region may trigger nuclear war.

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