2 Options to Prevent the Next Russian Invasion of Ukraine

Whenever Russia’s war on Ukraine ends, the challenge of securing the latter from aggression will just be getting started. Ukraine has a powerful neighbor that fundamentally rejects its sovereignty and is willing to inflict enormous costs on itself to snuff Ukraine out. Unless the war ends in some comprehensive peace settlement, which is unlikely, and as long as Russian President Vladimir Putin or anyone like him remains in power, Ukraine will need some effective means of deterring Russia from resuming the war in the future.

While there are many alternatives, two options for deterring Russia from a renewed attack are especially prominent in the debate ahead of next week’s NATO summit in Vilnius, Lithuania. The first is formal NATO membership for Ukraine, and the second is the so-called Israel option, which would entail building up Ukrainian military power with continued Western military aid—so that Kyiv’s strength and bristling arsenal alone can deter Russian aggression. Each option has its selling points, and both have serious drawbacks. Yet for all its problems, NATO membership may end up being the least-bad option, worth the hard diplomatic work it will take to achieve it.

If Russia’s battlefield misfortunes reach the level where Putin sues for a peace and makes significant concessions, say, a return to pre-2022 lines of control­—or almost unimaginable concessions, such as a return to pre-2014 lines of control—this would be a heroic victory for Ukraine and the West. But it would not solve Ukraine’s security issues once and for all. Even if the defeat ended Putin’s regime, it would still sting for Russia’s elite, which has mostly supported the war and shares some version of Putin’s disdain for Ukraine’s existence. The desire of many Russians to avenge a loss to Ukraine in some future gamble would likely remain to be exploited by future Russian leaders, as the history of enduring rivalries makes clear.

Until a robust, sustainable, and institutionalized regional security arrangement is established, the underlying conflicts of interest that broke out in violence before could do so again. A cease-fire that left Russia holding most of the Ukrainian territory that it occupies now would be even more fragile—more like a timeout than a transition to peace—and the steps necessary to prevent a recurrence would be daunting.

This is the paradox of security management familiar to post-war planners everywhere. On the one hand, Ukraine’s security needs will be undeniable. Even a chastened Putin (or a post-Putin Russia) would pose a genuine menace to Ukraine, which will need security help to restore military capacity lost in the war and to deter or prepare for another surprise attack. On the other hand, Russia will have its own security concerns about a revanchist Ukraine determined to claw back the rest of its stolen territory or punish Russia. Russia’s foolish invasion has galvanized Ukrainian nationalism, and Russia’s inept battlefield performance has underscored its own vulnerabilities. That means Russia will likewise seek to build up its own military capacity along the border with Ukraine even as Western diplomats work to restrain Ukraine’s own impulses. How well do the proposals for a postwar security arrangement manage these conundrums?

For the Ukrainian leadership, the optimal post-conflict security arrangement is simple: NATO membership, the sooner the better. Putin clearly draws a line between those parts of the former Soviet empire that now enjoy formal NATO membership—and thus the Article 5 commitments to collective defense by other members—and those that do not. He has scrupulously avoided infringing on the sovereignty of the Baltic States and former Warsaw Pact countries in NATO while running roughshod over Georgia, Moldova, and Ukraine. NATO’s critics harp on about a supposed lack of credibility for a NATO guarantee that would be hard to fulfill in an actual war, such as trying to defend the vulnerable Baltics. But the symbolism of a formal guarantee has surely proven more valuable than the critics have appreciated.

Article 5 would require that every NATO state overnight accept the risk that U.S. President Joe Biden has repeatedly insisted he will not accept: direct war with Russia.

Moreover, the alliance Ukraine would be joining would be stronger relative to the external threat than at any time in the past. For one, Putin proved more effective than decades of hectoring from Washington at persuading NATO member states to boost defense spending. And the addition of Finland—with Sweden in line to follow—gives NATO even more options to hold Russian military assets at risk and thereby dissuade Russian leaders from the kind of strategic folly that Putin exhibited in 2022.

To be sure, there are legitimate questions about whether NATO membership would be stabilizing or destabilizing. For starters, there is no consensus among the member countries on Ukraine’s accession and, as Sweden has learned, a single holdout can veto accession indefinitely—even for a country such as Sweden that easily meets membership standards, which Ukraine at this point does not.

Then there is the question of timing. If NATO membership is only available to Ukraine once the shooting stops, that creates an irresistible incentive for Putin to keep shooting indefinitely. If membership is available even before the conflict ends, that requires jettisoning the long-standing policy of rejecting the membership of states in ongoing military conflicts. It also requires determining which Ukrainian borders NATO’s Article 5 obligations pertain to. Are members pledging a commitment to Ukraine’s legal borders, which include all the land Russia stole in 2014? Ukraine’s pre-2022 borders? Or just the land it controls when the shooting stops?

Admitting Ukraine to NATO while the war is still ongoing would trigger the Article 5 obligation immediately. It would require that every NATO state, most notably the United States, overnight accept the risk that U.S. President Joe Biden has repeatedly insisted he will not accept: direct war with Russia. That said, the Article 5 commitment includes some wiggle room that leaves ambiguous how each member state would respond in a hypothetical invasion. Admitting Ukraine before the shooting stops surely would not be equivalent to declaring war on Russia, but it would bring the question of Article 5 commitments immediately to the fore. If Washington’s response is that it will only do under Article 5 what it has already been doing without it then what was gained by conferring membership status?

It also matters where the de facto lines of control end up. If Ukraine takes back all of its territory, including Crimea, it would have the upsides of aligning with international law and perhaps being easier to defend. The downsides of liberating Crimea include having to reincorporate a potentially restive province that has been Russified over the past decade. It would also maximize revanchist sentiment in Russia. Lines of control that leave Russia occupying stolen territory, on the other hand, might dampen Russian revanchism but would leave Ukrainian ambitions unsatisfied and, depending on local circumstances, could be very difficult to defend.

Once these matters are settled, similar questions to those that bedeviled NATO war planners throughout the Cold War would demand a response: Would Ukraine step up to defend itself or free-ride on the NATO guarantee? Past fears that NATO might become a chain-gang alliance where the parochial security squabbles of smaller states drag a great power into conflicts proved unfounded. Instead, NATO was more prone to the opposite collective action problem, whereby individual members lost interest in defense and relied on the U.S. security guarantee instead. Such free-riding was maddening and a persistent source of alliance friction, but it also helped ensure that the United States could impose its preferences on the rest of the bloc; in the end, NATO tended to dance to Washington’s tune precisely because the United States paid the piper.

Another canonical NATO war-planning problem would come to the fore with Ukrainian membership: how many non-Ukrainian NATO troops would need to be deployed on Ukrainian soil, and who would supply them? Again, formal membership would not guarantee that NATO allies would send troops to Ukraine. But as the Cold War experience showed, it is hard to make an Article 5 guarantee credible without some sort of tripwire. Here, U.S. domestic politics could play a spoiler role. Although there is still sufficiently sturdy bipartisan support for continued arms shipments to Ukraine and even pressure on the Biden administration to ramp up that support, this is counterbalanced by a strong bipartisan consensus against deploying U.S. combat troops to Ukraine. Thus, NATO membership would likely come with a rider that restricted U.S. rotations onto Ukrainian soil, a limitation not observed in other member states. Perhaps this could be finessed with a robust set of trainers and advisors, but it would be a tricky set of negotiations to conduct.

The myriad downsides to the NATO option have led some security analysts to propose an alternative, dubbed the Israel option (also sometimes called the porcupine option): build up the Ukrainian security force to the point where Ukraine is strong enough to deter any future Russian adventurism on the back of Western military aid and diplomatic cover, but without explicit guarantees that Western allies would join a fight on Ukraine’s behalf.

There are some undeniably attractive aspects to the Israel option, at least from the perspective of Washington and its NATO allies. The Israel option maximizes the role the West has most enthusiastically embraced: equipping, training, and diplomatically supporting a Ukraine that will fight for itself. And it minimizes the role the West is most skittish about: NATO troops fighting and dying in Ukraine.

Yet there are also downsides. First, implementing the Israel option is easier said than done, as more than 20 years of uneven success at something similar in Iraq and Afghanistan demonstrate. Moreover, in order for Israel itself to feel secure, the United States had to provide a qualitative military edge that gave Israel escalation dominance on air, sea, and land. Ukraine is nowhere close to enjoying such an edge today, and it would entail an enormous investment in advanced equipment to reach it. This is extremely expensive, likely requiring even more aid dollars than NATO membership.

Even if Western leaders can persuade their publics to meet the expense, they will likely remain reluctant to provide Ukraine with a true Israel option, because it would require equipping Ukraine with armaments that NATO has so far refused to provide. Israel enjoys air superiority over its regional adversaries and has a deep strike capability that covers the entire terrain of every adversary—a capability that Israel has exercised repeatedly over the decades. An Israel-option Ukraine could penetrate deep into Russian territory with sustained air and missile strikes, a far more potent capability than the symbolic drone pin-pricks or sabotage incidents seen to date. Such a Ukraine would be able to inflict reprisals on Russian territory as payback for the horrific atrocities Putin has inflicted on Ukrainian cities. If Russia fears NATO troops on its borders, it has all the more reason to fear an unrestrained Ukraine capable of acting like Israel. Paradoxically, the NATO membership for Ukraine that Putin supposedly fears would go a long way to constraining Ukrainian actions.

Moreover, the Israel option requires a long-term commitment, and that, in turn, depends on who is in power in Washington and Kyiv. Israel has depended on decades of extraordinary support from the United States, support that remained robust regardless of which party controlled the White House and which party ruled in Israel. The political basis for U.S. support for Ukraine is presently high, but even its post-invasion peak didn’t reach the level of support for Israel over the decades. How viable is the Israel option for Ukraine if former U.S. President Donald Trump wins the 2024 presidential election? Or if Ukrainian President Volodymyr Zelensky is replaced by a less capable leader? Or if Ukrainian efforts to tamp down corruption falter?

Most ominously, if the conventional wisdom about an Israeli nuclear arsenal is correct, Israel itself believes that a credible Israel option requires more than conventional armaments. Will Ukraine believe that deterrence is adequate without a NATO guarantee and without a nuclear arsenal of its own to provide the ultimate deterrent?

These difficulties have led some to propose a hybrid: continued Western support augmented by security assurances by the United States and the major European powers—without formal NATO membership. This has the undeniable advantage of being easier to achieve than either membership or a full-blown Israel option. Beyond that one selling point, however, the hybrid formula has all of the drawbacks of the two alternatives without any of the corresponding advantages. It’s unlikely to be stabilizing in the long run.

In short, even after the shooting stops, Ukraine will need security help to restore military capacity lost in the war. That help must make Ukraine strong enough to deter the Russians but not so strong as to be totally intolerable to them. Getting that sort of balance right was a central priority for NATO when it rearmed Germany in the 1950s. NATO leaders took pains to mitigate the security dilemma that German rearmament posed, striving toward a Germany strong enough to help deter the Soviets but not so strong that it triggered a Soviet preventive invasion. At the same time, German rearmament was encased in a larger security arrangement designed to keep ambitions in check. Getting the balance right is exceedingly challenging, as the raft of crises and brinksmanship in the 20 years after World War II made clear. Getting it wrong can produce an even bigger catastrophe, as happened with the failed peace that followed World War I.

Of the options on offer, NATO membership with an Article 5 guarantee of de facto borders represented by the lines of control may be the hardest to negotiate but the most stabilizing in the long run. NATO provides the best chance at both reassuring and restraining Ukraine, should the shooting stop with both sides unhappy about the division of territory. The attractions of the Israel option are obvious, but there are unappreciated drawbacks. The drawbacks of NATO membership are obvious, but there are unappreciated benefits.

Putin and his cronies will not like either option. Indeed, they misleadingly claim they launched the war to prevent Ukraine from joining NATO in the first place. However, once faced with realistic alternatives, membership for Ukraine might end up being the least provocative choice precisely because it offers a tight institutional framework to manage Ukraine’s postwar ambitions.

Whichever option for Ukraine’s security you pick, the demands on the United States are considerable going forward. As we learned at great cost in the 1940s, when the United States ignores security threats in the short run, it ends up having to shoulder more risk and commitment in the long run. The inconvenient truth about the failure to deter Putin from invading Ukraine in the first place is that Americans can no longer pretend that there is a good option out there that does not involve a significant amount of risk and U.S. commitment.