By Eric Vandenbroeck and co-workers

Do Realists Hold the Solution to a World in Crisis?

For the last four years, policymakers in Washington and European capitals have been consumed by a single question: how to respond to Russia’s full-scale invasion of Ukraine. Their focus is understandable. Russia’s attack on its neighbor is the greatest threat to European security since U.S. and Soviet tanks stood off in Berlin over 60 years earlier. As a result, NATO allies have sent Ukraine hundreds of billions of dollars in military, economic, and humanitarian assistance to prevent it from losing the war and collapsing. The Europeans have received waves of refugees and, together with the Americans, enacted tough sanctions against Russia. Facing pressure from U.S. President Donald Trump, leaders across the alliance have held a series of summits to try to end the fighting.

But the resolution of the conflict, whatever its contours, will not put an end to the forces it has unleashed. Indeed, a cease-fire could mark the start of an even more dangerous era. Once the guns fall silent, Russia and Ukraine will still be locked in a tense confrontation. Moscow will rearm and likely increase its destabilizing activities across the continent. Europe will keep spending more on defense, disavowing the integration it once pursued with Russia and adopting a more hawkish posture. The United States might try to disentangle itself from the standoff, but its economic and political stakes in Europe will make a full withdrawal impossible. There will, in short, be little communication and much suspicion between NATO and Russia.

This is hardly a recipe for a new long peace. Quite the opposite: the risk of a direct conflict between Russia and Western states will remain unacceptably high. With prolonged distrust, ongoing military buildups, minimal communication, a gutted security architecture, and continued Kremlin provocations, there will be no shortage of scenarios in which a small spark could lead to a continental conflagration. The odds of war could grow especially high if the transatlantic alliance frays or even collapses.

Policymakers in the United States and Europe must not allow that to happen. Even as they struggle to end Europe’s current war, they must begin working to prevent the next one. NATO should accept that there’s no returning to the pre-2022 world and develop new ways to manage its relationship with the Kremlin. Otherwise, the Americans and the Europeans might find themselves in a third global conflict, with the continent once again the central battlefield.

 

Point Of No Return

For most of the post-Cold War era, Russia and Western states had working relations. After their confrontation ended, the two sides established a latticework of institutions, diplomatic forums, and exchange programs aimed at fostering mutual understanding and preventing conflict. They created the inclusive and consensus-based Organization for Security and Cooperation in Europe, a continent-wide forum for dialogue based on shared norms and institutions. They set up various mechanisms for interaction and even cooperation between NATO and Russia. And they implemented a host of arms control agreements and military confidence-building measures.

This framework was never perfect, and it nearly collapsed when Russia annexed Crimea and invaded eastern Ukraine in 2014. But it was broadly successful at preventing a return to a Cold War–style standoff. The economies of the European Union and Russia grew increasingly interdependent: the former received cheap energy and other raw materials, and the latter gained large amounts of foreign direct investment, Western knowledge, and sophisticated consumer products. Millions of people began traveling back and forth between Europe and Russia each year via trains, land crossings, and dozens of daily flights. Russia was part of the EU’s educational standardization, which meant that degrees from its universities were recognized across the continent. Moscow was a party to the Council of Europe - the continent’s human rights, democracy, and rule-of-law organization - and its multitude of conventions.

But when Russian tanks started rumbling toward Kyiv on February 24, 2022, this system fell apart. The NATO-Russia Council was immediately suspended and subsequently abolished. Moscow withdrew from the Council of Europe. The Organization for Security and Cooperation in Europe still technically exists, but it now serves as a forum for Russia and NATO countries to exchange mutual ritualistic condemnations and accusations. EU-Russian trade has nosedived: in 2024, the total trade in goods between the EU and Russia amounted to around $80 billion, compared with around $300 billion only three years before. Aside from recent U.S. engagement on Ukraine, Western officials speak to their Russian counterparts very little, if at all, on any level. Educational exchanges have almost entirely ceased. The land crossings between Russia and its NATO neighbors are all either closed or heavily restricted. The only direct flight between Moscow and countries in Europe, aside from Belarus, is an Air Serbia flight that departs from Belgrade.

At first, Western allies told themselves that these steps were temporary. But after four years, it is apparent that this shift is permanent. Although some past wars - for example, World War II -have ended in reorderings in which the trends and systems that existed before and during the conflict were upended, the war in Ukraine is unlikely to produce such a moment. Neither side seems capable of achieving an absolute victory, which means the Russian regime is extremely unlikely to collapse and be replaced with a more liberal government, as happened in Germany and Japan after their defeats. For at least as long as Russian President Vladimir Putin is in power, his country will remain a personalist autocracy. Its economy will be weakened, but unlike the Soviet Union’s command economy, it will not collapse.

With so many of its people dead and wounded and many more alienated by both domestic propaganda and Western policy and rhetoric, Russia will be angry and resentful toward the United States and Europe after the war in Ukraine is over. Moscow will have every motive to rearm and regenerate its forces. Some of those forces will be stationed in and around Ukraine, but many will be deployed along NATO’s eastern flank in order to tilt the military balance in Russia’s favor. According to Finland’s 2025 military intelligence review, after the war, Moscow is expected to more than double the number of troops it stations along NATO’s northern frontiers - from 30,000 to 80,000 - and to modernize key capabilities in the region.

The old Russia, which at least paid lip service to cooperation, is not coming back. But prewar Europe is also long gone. The allies are in a process of remilitarization. They are massively increasing defense spending. Some of them are contemplating reinstituting mandatory national military service. Others are distributing manuals on what to do in case of an invasion. European countries will also position more troops near the NATO-Russian frontier: since Finland and Sweden joined NATO in 2023 and 2024, respectively, the alliance has been planning several new multinational military formations in the region. Meanwhile, officials have reengineered their countries’ economies away from being dependent on Russia, particularly for energy imports. European policymakers are personally - and justifiably - mortified by Russia’s ongoing aggression and atrocities in a country that borders four members of the EU and NATO. As a result, they have adopted hard lines on Russia and are deeply skeptical about the prospects for any engagement.

For now, it is safe to conclude that the continent’s environment after the war in Ukraine ends will not be dramatically different from the unstable environment of today. NATO allies and Russia will remain largely cordoned off from each other, with no functioning mechanisms for intergovernmental or intersocietal communications. They will struggle to understand each other’s decisions and will assume the other side is hostile in intent.

 

On The Brink

As relations have deteriorated, policymakers in both Europe and Russia have warned that they are on a path to war. A July 2025 French National Strategic Review warned of the “risk of open warfare against the heart of Europe” by 2030. Germany’s defense minister said in November that Russia would be ready to attack by 2029 and observed that “certain military historians” were saying that the continent had already lived through its “last peaceful summer.” In December, NATO Secretary-General Mark Rutte announced that Russia could attack a NATO country in the next five years and that member states “should be prepared for the scale of war our grandparents or great-grandparents endured.” Moscow, meanwhile, has framed NATO as an aggressive, expansionist bloc. In February 2024, Putin warned Russians that NATO is “preparing to strike our territory.”

It would be foolish to rule out a deliberate, premeditated Russian attack against NATO. Militaries can and should prepare for even low-probability events when the stakes are high, as they are here. The most plausible conflict scenarios, however, do not dovetail with European leaders’ current rhetoric. It has been clear since the early 1990s that Moscow considers NATO - and particularly the United States - the superior conventional power, destined to win in a direct fight against Russian forces. As long as NATO maintains a relatively united transatlantic front, a deliberate, opportunistic Russian attack on the alliance is a remote prospect.

But there are quite plausible ways that Russia and NATO could end up at war, even if the transatlantic alliance remains intact. Consider, for instance, Moscow’s persistent gray zone actions, such as the sabotage of critical infrastructure and targeted assassinations. So far, the alliance has been restrained in responding to these provocations. Yet NATO officials increasingly think this timidity merely emboldens the Kremlin and are therefore considering “being more aggressive” in response - as Admiral Giuseppe Cavo Dragone, the chair of NATO’s Military Committee, put it in November. A Russian airspace incursion or damage to an undersea cable could now engender a much more assertive response, such as seizing a Russian tanker.

If that did happen, a crisis might quickly ensue. Given the mutual suspicion and lack of communication between the two sides, the Russian military’s general staff and its political masters in the Kremlin would probably not interpret NATO’s move as purely reactive or defensive. Moscow would thus counter, possibly by engaging in destructive cyberattacks on civilian and military targets. Both NATO and Russia would then start raising the readiness levels of their conventional forces, calling up reservists, and moving key capabilities toward their shared frontiers. The United States would likely surge assets to Europe, including long-range air and ground-based missile systems. Russian strategists believe that these are the exact systems that Washington would use early in a conflict to hit Russia’s leadership and military targets - an outcome they greatly fear. Throughout the war in Ukraine, Kyiv has used high-end U.S. systems to strike important military targets in Russia, exposing the country’s poor defenses. Moscow might therefore respond to the arrival of U.S. long-range weapons with a preemptive attack against them.

That is just one path to war. Another might begin with Russia’s snap military exercises. These drills are not announced in advance, and foreign countries can easily misinterpret them as preparations for an attack. NATO member states are particularly suspicious that such drills could serve as cover for a new Russian military operation after Moscow used military exercises in early 2014 and late 2021 as a pretext for massing forces on Ukraine’s border. Given the minimal communication between the two sides, high political tensions, and large numbers of forces arrayed in proximity, NATO leaders could conclude that Russia was readying a new assault if Moscow were to suddenly conduct such an exercise near the Baltic states. To avoid Western Europeans and Americans hemming and hawing about whether to respond, Estonia, Latvia, or Lithuania might have an incentive to preemptively strike Russian forces before they cross the border.

A NATO-Russian war could also expand out of a second, full-scale armed clash in Ukraine. Conflict spillover has been a risk since the start of Russia’s 2022 invasion. There have even been close calls, including when an air defense missile, later identified as Ukrainian, strayed into Polish territory and killed two people in November 2022. If a future Russian-Ukrainian cease-fire broke down, the risk of escalation that ensnares one or more neighboring allies would likely be even higher. European countries have indicated that they could intervene directly on Ukraine’s behalf were Russia to attack again.

Finally, NATO and Russia could come to blows over other states in the region, particularly Belarus. The country is Russia’s most important treaty ally: it provides a modicum of strategic depth for major Russian population centers, hosts several Russian military installations, and is now home to some of Moscow’s nuclear weapons. Like any authoritarian state on a geopolitical fault line, Belarus is also a potential tinderbox, since any major domestic political change could transform the country’s external alignments. After Alexander Lukashenko, the country’s Russia-friendly president who has ruled since 1994, was declared the winner of the rigged August 2020 elections, hundreds of thousands of Belarusians took to the streets to protest in support of the more pro-Western opposition. At the time, Moscow had the patience and confidence to sit on the sidelines, providing verbal support as Lukashenko’s forces violently suppressed the demonstrations. But if Lukashenko or his chosen successor were in the same situation, the Kremlin likely would not be comfortable waiting out the protests. After enraging Ukrainians with its invasion and transforming Kyiv into an enemy, Moscow would not accept the loss of Belarus.

To ensure that a Moscow-aligned regime survived mass Belarusian protests, Russia would not hesitate to move its national guard or airborne units into its neighbor to quell the unrest. As it did in 2020, Belarus would put its armed forces on high alert. But unlike then, it might now reposition some units toward its borders with Lithuania and Poland in response to fears - justified or not - that those neighbors were supporting the opposition. The two countries might call for NATO consultations under Article 4 of the alliance’s founding treaty, mobilize their reservists, and move their forces closer to the borders with Belarus. NATO would probably ready its rapid-reaction forces for deployment to the area. Russia, fearing conflict, would surge assets into its Kaliningrad exclave by air and sea. Tensions would reach a fever pitch. If either side made a wrong move, war could result.

 

Denial By Deterrence

After the war in Ukraine is settled, some Western officials might be tempted to roll back defense spending pledges and immediately move to negotiate a broader détente with Moscow. But that would be a major strategic error. As a revisionist power with deep, existential insecurities and firm views about how to address them, Russia is not interested in security and stability on NATO’s terms. On the contrary, it will probe and prod at any openings that it detects, real or imagined. That means NATO’s top priority should be eliminating any such openings by shoring up deterrence.

To do so, the United States and its allies should start by getting their relationship on a firmer footing. This will not be easy. Tensions between the Trump administration and European governments have nearly boiled over on multiple occasions, including because of U.S. designs on Greenland. A full break between the United States and its allies would leave the continent much more vulnerable to Russian aggression. Moscow has been careful to avoid a direct conflict with NATO thanks, in large part, to Washington’s military presence in Europe and its clear commitment to the continent’s defense. Without that, Putin might become less cautious. Open fractures must therefore be avoided.

Some members of the Trump administration may care little about Europe’s fate and thus about repairing the rupture. But anyone who thinks Washington would escape a war between Russia and the continent is mistaken. The United States cannot remain prosperous and secure without a stable and secure Europe. Transatlantic linkages are hard-wired into the U.S. economy, and American geopolitical heft would be greatly diminished if NATO collapses. Washington will inevitably be dragged into a conflict with Russia if deterrence fails.

There is reason to hope the two sides will find a new, mutually acceptable equilibrium. Europe increasingly accepts that the United States will not revert to the status quo ante, in which it took primary responsibility for defending the continent. But Washington will have to play a large role in European security until its allies are mostly capable of defending themselves. European NATO members have the resources and industrial capacity required to build formidable militaries, and they have started to use them to that end. But they can move only so fast, and if Washington abandons Europe before it is ready, Russia might take more risks.

In addition to putting up a united transatlantic front, European states will need to deliver on their ambitious plans for new spending and new capabilities. But rather than spreading their defense euros thinly on a wide variety of capabilities, the continent needs to be targeted and specific. Its states should have a clear idea about what they are trying to prevent and what will actually intimidate their adversary. They should, in particular, recognize that deterring Moscow does not require being capable of repelling any act of aggression under any circumstances. In fact, trying to do so might encourage Russia to take action to prevent a decisive shift in the military balance. Instead, Europe should have enough forces forward deployed to both raise the cost of a potential attack and make escalation to a continent-wide fight inevitable. Its countries, in other words, have to calibrate their posture to reinforce deterrence without exacerbating Russian threat perceptions.

 

 

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