As the world looks on while Ukrainians fight for their lives and their freedom, many feel a burning desire to do more to support them. The problem is not a lack of forces or resources—it is fear of provoking a wider, perhaps nuclear, war with Russia. That fear is why U.S. President Joe Biden and other NATO leaders have consistently made clear that they will not intervene directly in the conflict, instead limiting their help to weapons, money, intelligence, and sanctions. As devastating as events in Ukraine are today, a nuclear war with Russia could kill more people than Ukraine’s entire population of roughly 44 million.

NATO leaders understand that they must walk this fine line between aiding Ukraine and risking war with Russia, but they have no theory of how to do it. The German and French governments hem and haw about whether to provide Ukraine with tanks. When Poland proposed a plan to transfer MiG-29 fighter aircraft to Ukraine, the United States refused. U.S. Defense Department spokesperson John Kirby warned that it “raises serious concerns for the entire NATO alliance” and therefore was not “tenable.” Yet the United States was already shipping Javelin antitank missiles and Stinger surface-to-air missiles. Soon after, it began sending other weapons, including M777 howitzers and now HIMARS multiple-rocket launchers. What is the difference? Those weapons do more to strengthen Ukraine’s combat power than MiG-29s, so the theory cannot be that Russia reacts more strongly to policies that do more harm to its interests. Why, then, missiles and artillery but not planes? The answer is that there is no answer. It is simply arbitrary.

NATO needs a strategy predicated on a theory of what it can do to aid Ukraine without widening the war to a direct conflict between it and Russia. Lessons from past crises point to the principles that should guide such a strategy. History shows that NATO would recklessly risk war only by crossing two Russian redlines: openly firing on Russian forces or deploying organized combat units under NATO-member flags into Ukraine. As long as NATO stops short of unmistakably crossing those lines, it can do more to help Ukraine at an acceptable risk of war.

Arms transfers and sanctions are both wholly consistent with this approach, so it is tempting to conclude that NATO members are doing all they can. They are not. They should build on current policies by dispensing with arbitrary limits on the types of conventional weapons they are providing Ukraine and expanding sanctions. Moreover, there is a third way to support Ukraine besides arms and sanctions—one that NATO is neglecting. It is time for NATO to encourage, organize, and equip its soldiers to volunteer to fight for Ukraine.

WALKING THE LINE

NATO should pursue a strategy of going as far as possible in Ukraine without plainly crossing Russia’s redlines—meaning refusing to openly attack Russian forces or send combat units into the country. The United States prevailed in the gravest crises of the Cold War by using this approach.

The Cold War’s first major showdown—the Berlin blockade of 1948–49—evinced this strategy. Although easily able to overwhelm U.S., British, and French troops in what would become West Berlin—an enclave deep inside Soviet-occupied East Germany—Soviet leader Josef Stalin did not seize the territory. To do so would have meant attacking those troops and thus provoking war. Instead, he imposed a blockade that choked off food and coal for two million Berliners. When Soviet troops blocked the roads and railways, Western leaders declined to attack them to reopen supply corridors. They resorted to an airlift instead, betting that Stalin would not attack defenseless transport aircraft. In the end, the vaunted Berlin airlift succeeded.

More than a decade later, American leaders decided to impose a blockade in lieu of launching an open attack—this time, during the Cuban missile crisis in 1962. Angered by the Soviet Union’s attempt to sneak nuclear missiles into Cuba and Moscow’s lies about it, U.S. President John F. Kennedy was initially inclined to destroy the missiles with airstrikes. He and others around him, however, decided the risks were too great. Director of Central Intelligence John McCone deemed airstrikes too risky, writing in a memo that the “consequences of action by the United States will be the inevitable ‘spilling of blood’ of Soviet military personnel.” He went on: “This will increase tension everywhere and undoubtedly bring retaliation against U.S. foreign military installations.” Soviet Premier Nikita Khrushchev recognized this, too. According to a transcript of his remarks at a Soviet Presidium meeting, he feared that a U.S. attack would spark a war: “The tragic thing—they can attack, and we will respond. This could escalate into a large-scale war.” Kennedy chose neither to attack nor to accept the missiles as a fait accompli. He instead blockaded Cuba. In history’s gravest nuclear crisis, neither leader ordered an attack.

It is time for NATO to encourage, organize, and equip its soldiers to volunteer to fight for Ukraine.

One attack did occur, however, when Soviet generals on the ground in Cuba decided to launch surface-to-air missiles to shoot down an American U-2 spy plane that had entered Cuban airspace. The attack killed U.S. Major Rudolf Anderson, Jr., the pilot. Khrushchev’s fears of war peaked at that moment, and Moscow chastised the generals who carried out the attack. Before retaliating, Kennedy gave diplomacy one last chance. Shared fears about the implications of that shootdown led both sides to make concessions that helped resolve the crisis. In the end, the United States prevailed by taking risks without attacking.

The United States and the Soviet Union also engaged in proxy wars to avoid attacking each other directly and starting World War III. Both countries used large-scale arms shipments and sometimes soldiers fighting as volunteers to support local forces. Designed to avoid escalation, such covert wars are a common tactic in international politics. During the Korean War, Soviet pilots secretly fought in the Chinese air force. Soviet arms equipped North Vietnam, and Soviet soldiers even operated surface-to-air missile batteries against U.S. aircraft. Despite its losses, the United States decided to tolerate this Soviet participation rather than widen either war. The Soviets also allowed similar behavior from the United States on other battlefields. When the Soviet Union invaded Afghanistan, for example, the United States armed and financed the mujahideen resistance. The Soviet Union eventually withdrew. As recently as 2018, Russian Wagner Group mercenaries in Syria unsuccessfully attacked U.S. forces operating alongside Kurdish forces. The United States did not treat it as an attack by the Russian government.

HOW FAR CAN NATO GO?

These examples underscore that pushing as far as possible without openly attacking is often the best way to compete while managing escalation risks. Creative policymaking can engineer options that achieve objectives without crossing redlines, thus preventing a wider war. Providing intelligence that Ukrainian forces use to kill Russian soldiers is not the same as NATO openly attacking Russia, nor is support in cyberspace. Lithuania’s restrictions on Russia’s use of its territory to ship goods to Kaliningrad meet this standard. Even enlarging NATO to include Finland and Sweden and deploying forces eastward to defend NATO members bordering Russia entail acceptable risks; such actions do not constitute an attack on Russia. In fact, there is good reason to think that NATO can do even more in Ukraine without provoking a wider war.

Some believe that Russia’s nuclear weapons and greater interests in Ukraine give it the advantage over NATO. This is mistaken. It is true that NATO leaders prioritize avoiding war with Russia over aiding Ukraine, but it is just as true that war with NATO would cost Russia far more than would abiding most forms of aid to Ukraine. After all, Russia is already struggling mightily against Ukraine. It cannot simultaneously win a conventional war with NATO. And no one would win a nuclear war.

Interests alone do not determine who has the advantage when both sides wish to avoid war. Instead, the advantage goes to the side that puts the other in the difficult position of choosing whether to escalate or accept a limited defeat. The side that must start the war is in the more difficult position. Russia has tolerated NATO’s sanctions and arming Ukraine for precisely that reason.

To be sure, it would be wrong to conclude that NATO can get away with anything. Most important, Russia will not accept NATO openly attacking Russian forces. If NATO can shoot down a Russian aircraft with impunity—for instance, to enforce a no-fly zone over Ukraine—where would it end for Russia? Why would NATO not keep attacking? How could Russia credibly threaten to retaliate for the second plane after not doing so for the first? What about the third? The tenth? What, then, would stop NATO from bombing Russian forces in Ukraine? Russia cannot allow the precedent of consequence-free attacks on Russian forces.

Borders are Russia’s other vital redline. NATO forces openly operating in Russia are plainly unacceptable, and NATO should also rule out deploying organized combat units in Ukraine. Sending units to Ukraine to fight Russian forces risks war. NATO troops in Ukraine for purposes other than combat—such as deterring Russia from advancing into certain areas—would do less to strengthen Ukraine on the frontlines. And their presence would risk Russian attacks against them, intentional or unintentional.

CALL TO ARMS

Within these limits, there are three primary ways to aid Ukraine. The first is arms, and on that, NATO can do more. The current limits on NATO arms to Ukraine are not grounded in any theory or strategy. NATO can provide Ukraine with modern tanks, fighter aircraft, advanced surface-to-air missiles, and more at acceptable risk. The second is sanctions, and NATO can do more there, too—starting with further curtailing European imports of Russian natural gas.

The third way is by supplying foreign volunteers—a strategy NATO has largely neglected. Although some volunteers are already there fighting as individuals or in Ukraine’s International Legion, NATO members should encourage, equip, and fund their soldiers and veterans who are willing to fight for Ukraine. To limit the risk of war with Russia, these soldiers would fight wearing Ukrainian uniforms under the Ukrainian chain of command.

States recruit foreign soldiers to gain expertise and to forestall military defeat. In Ukraine’s case, if used adeptly, foreign volunteers could help Ukraine bolster its proficiency with combat skills that take years of training and expertise to master, and use advanced weapons more quickly and effectively. This is essential as Ukraine exhausts its Soviet-era stocks and transitions to more advanced NATO weapons. In the longer run, numbers also matter. If Ukraine turns the tide against Russia, Moscow may react by fully mobilizing for war, banking on its larger population to ultimately overwhelm Ukraine in a war of attrition. A growing stream of foreign volunteers would upend Russia’s calculation that it could win a long war. NATO has already removed the upper limits on the quantities of weapons Ukraine can bring to bear. It is time to do the same for the troops on the ground.

The benefits of organizing volunteers exceed the risks. Data on more than 230 cases of states recruiting foreign soldiers—often amid ongoing war—supports this conclusion. According to Elizabeth Grasmeder, who collected and analyzed this data, not once did recruiting foreign volunteers provoke the state fighting against those soldiers to go to war with the state supplying them. Only a few cases led to limited attacks to discourage the recruitment.

Russia cannot allow the precedent of consequence-free attacks on Russian forces.

Certainly, this policy comes with costs and challenges. Serious obstacles to interoperability could emerge involving languages, communications equipment, ammunition, and spare parts. Yet Ukraine faces some of those difficulties already as it exhausts the old Soviet equipment it is using and transitions to NATO-provided weapons. Because Ukraine needs trained soldiers more than brand new recruits, NATO states must make it easier for soldiers to temporarily resign to fight for Ukraine. They must ensure that medical care and other benefits will be ready for these soldiers—and that volunteers can smoothly rejoin when they return. Their prospects for promotion should reflect their hard-won combat experience. The hardest part of this policy will be accepting casualties among the volunteers without retaliating. This is why they must truly be volunteers, unlike the soldiers Russia ordered into Crimea and the Donbas as “green men” in 2014. Not all NATO members will embrace these obligations, but with U.S. participation, some would be enough.

To mitigate risks, NATO should start small by focusing on expertise more than numbers. Russia will be loath to start an unwinnable war with NATO over a few hundred more volunteers fighting for Ukraine—even if organized more purposefully by NATO governments. Tacitly tolerating their deployment will make it harder for Russia to deter the next hundreds, which gradually become the next thousands.

Ever since proposals for a no-fly zone failed, the desire to do more for Ukraine has struggled to crystallize around a prudent and realistic plan. Foreign volunteers is the right policy to explore. Coupled with abandoning unnecessary limits on which arms NATO members send to Ukraine, this is how NATO can more effectively support Ukraine without starting World War III.

You are reading a free article.

Subscribe to Foreign Affairs to get unlimited access.

  • Paywall-free reading of new articles and a century of archives
  • Unlock access to iOS/Android apps to save editions for offline reading
  • Six issues a year in print, online, and audio editions
Subscribe Now