By Eric Vandenbroeck and co-workers

Europe’s Bad Nuclear Options

The early months of the second Trump administration have left Europe adrift. The continent was already reeling from the war in Ukraine and increasingly worried about the specter of Russian aggression. Now, new leadership in Washington is casting doubt on its commitment to the defense of European allies.

In the eyes of Europeans, even the U.S. nuclear umbrella, which for decades has shielded the continent from outside threats, no longer seems fully dependable. “I want to believe that the United States will stay by our side,” French President Emmanuel Macron said in March. “But we have to be prepared for that not to be the case.”

The way forward, Macron has argued, is to protect the continent from attack without relying on the deterrent power of American nuclear weapons. France’s contribution, he has suggested, might be to put its own nuclear arsenal in the service of its European neighbors.

It is too early to tell what will come of the French president’s offer. A similar proposal that Macron made in 2020 was ignored in other European capitals. But the continent’s geopolitical predicament has grown much direr in the years since, and the probability of an attack on European members is now at a level not seen since the late 1970s. Given that reality and the seeming indifference of the Trump administration to it, the continent needs to rethink its deterrence strategies. If the American nuclear umbrella is no longer open, Europe might need one of its own. Ironically, this would run counter to U.S. President Donald Trump’s ambition, stated in 2017, to “de-nuke” the world.

The credibility of any nuclear deterrent rests on two pillars: having the right capabilities and having the resolve to use them. Judged by those criteria, neither Macron’s proposal nor any other option for an independent European nuclear deterrent currently passes muster. But even if the moment for Europe to decouple its security from that of the United States has not yet arrived, the continent’s leaders must prepare for the possibility that it may before long. And that means beginning to take serious stock of their nuclear options. In the short term, doing so will signal that Washington needs to take Europe’s deterrence concerns seriously. But it would also lay a foundation on which Europe could build should its fears of abandonment by the United States really come true.

 

From Protest to Proliferation?

Historically, most European countries have viewed nuclear weapons with skepticism and, in some cases, outright hostility. Antinuclear sentiment peaked in the 1980s, when NATO’s “dual track” decision, which included plans to station American intermediate-range nuclear weapons in Western Europe, set off massive protests in cities across the region. Popular opposition was fueled in part by the belief that U.S. nuclear weapons were not a deterrent against Soviet aggression, as NATO leaders argued, but a vehicle for reckless provocation and warmongering. The 1983 film The Day After offered a fictionalized preview of what might lie in store: a U.S.-​Soviet confrontation in Berlin spiraling into a small-scale nuclear war and, eventually, a global nuclear wipeout. Among the record number of dystopian nuclear-themed works of science fiction to have come out of the 1980s, many played on such fears.

In reality, what followed was not Armageddon but détente. The Americans and the Soviets agreed to limit their arsenals, and those agreements held after the Soviet Union fell and Russia took its place. As the Cold War receded into history, fears of nuclear war abated.

But in European policymaking circles, resistance to the logic of nuclear deterrence persisted. Outside Europe’s two nuclear powers, France and the United Kingdom, European officials and thinkers still tend to associate all things nuclear with destruction more than with deterrence.

Even so, the war in Ukraine has brought the nuclear issue back into focus, mainly in light of a renewed and growing nuclear threat from Russia. Part of the problem is the sheer size and potency of Russia’s arsenal of around 5,580 nuclear warheads. It is unclear how many of those warheads are meant to target central or western Europe. But the dozens of nuclear warheads Russia has stationed in Belarus are cause for concern, as they could easily strike NATO countries such as Latvia, Lithuania, and Poland.

More worrying than the arsenal itself, however, is Russia’s potential willingness to use it, including as a means of coercion and blackmail. Russian President Vladimir Putin’s repeated nuclear threats against Ukraine and its European supporters portend trouble for the rest of the continent, particularly in conjunction with the ongoing reorganization and modernization of Russia’s armed forces. Russia appears to be reorienting its military capabilities and strategy toward the possibility of protracted conflict with Europe. It also aims to increase active military personnel from 1.3 million to 1.5 million by 2027, raising the possibility of a return to Soviet-style mass mobilization.

Even as the geopolitical danger from the East has increased, the protection afforded by the American nuclear umbrella no longer seems guaranteed, at least not since Trump took office for the second time in January. Of course, the United States still has the ability to provide Europe with a credible nuclear deterrent. What is increasingly uncertain is whether, under Trump, it still wants to do so. Trump and those around him have repeatedly suggested that the United States might not come to its allies’ rescue if they were attacked, musing about pulling U.S. troops out of Europe and implying that Washington might not defend NATO members that do not spend sufficiently on their own defense.

To be sure, such rhetoric may just be an attempt to pressure European allies into higher defense spending. To actually push those allies out from underneath the American nuclear umbrella would undermine the United States’ status as a superpower, alienate some of the most important partners in its geopolitical competition with China and Russia, reduce its leverage over Europe, and perhaps open the door to nuclear proliferation on the continent. But security experts could find themselves in a similar position to that of economists: despite near-total expert consensus that tariffs will spark a trade war and hurt the U.S. economy, Trump plowed ahead. In the economic realm, such missteps are harmful. In the domain of national security, the ramifications could be existential.

The principle of collective defense enshrined in NATO’s founding treaty “derives its credibility less from the formal treaty than from a belief among the members that they are all prepared to come to one another’s defense. Potential aggressors must believe the same thing. Europe’s entire post–Cold War security architecture rests on this belief. To throw it into doubt risks undermining the entire system from within and without.

A French Navy nuclear attack submarine in Halifax, Canada, March 2025

So far, European debates on how to establish deterrence without U.S. assistance have centered on conventional, non-nuclear military capabilities, and understandably so. The limited conventional military capabilities of European NATO members could tempt Russia into carrying out a limited attack - seizing a small piece of territory from one of its Baltic neighbors, say, or engaging a European military vessel - with the expectation that it would not suffer any serious consequences. If such an attack took place and Europe lacked the means for an appropriate military response, NATO’s credibility would be shattered. Recognizing that danger, most European countries have pledged significant increases in defense spending. It will likely take several years for those investments to fill the gaps, but at least the necessary political decisions have been made and there is broad public support for them.

A potential European nuclear deterrent is a different matter. European politicians have sporadically expressed concern about the nuclear threat from Russia, and defense experts have begun discussing Europe’s nuclear options more seriously. What is lacking, however, is an informed public debate, despite Macron’s recent proposal.

The conditions for such a debate are better than they have been in years. Before Russia’s full-scale invasion of Ukraine in 2022, polling indicated that in four European countries that hosted U.S. nuclear weapons - Belgium, Germany, Italy, and the Netherlands - a plurality of respondents opposed such hosting arrangements. By contrast, in a March poll of nine European countries, 61 percent of respondents said they would welcome a French nuclear umbrella covering the entire continent.

An extended nuclear deterrent of this type, provided by France but ideally also supplemented by the United Kingdom, would certainly merit closer scrutiny if the United States further diluted or even disavowed its security guarantees. Two other options, which seem less pertinent because they are even more controversial, also deserve attention. One is a collective nuclear deterrent: that is, an arsenal that would be controlled by a pan-European institution. The other is the acquisition of nuclear weapons by additional European states. If Europe chose any of these paths, it would need to meet two criteria to make its nuclear deterrent credible. First, its arsenal would have to be sufficiently large, technically sophisticated, and capable of surviving a first strike. Second, whoever controlled the arsenal would have to demonstrate a willingness to use it.

 

Sovereignty vs. Solidarity

Of the three options, only one has been seriously discussed so far: an extended nuclear deterrent provided primarily by France, with complementary support from the United Kingdom. The new German chancellor, Friedrich Merz, has indicated interest in such an arrangement, even if he has said it would serve only to supplement American nuclear guarantees, not to replace them. And in May, France and Poland signed a treaty to deepen their security ties, a step that Polish Prime Minister Donald Tusk described as a step toward a potential French nuclear umbrella for his country.

As of today, however, French and British nuclear capabilities raise serious credibility concerns. Some 290 French nuclear warheads are ready for deployment; the United Kingdom can provide another 225. Taken together, that is a mere ten percent of what Russia can field.

Deterrence is no simple numbers game, but a gap this wide is a clear liability, for reasons of both objective and perceived weakness. For one thing, it effectively restricts European allies to what nuclear experts call “deterrence by punishment.” Such deterrence rests on the threat of overwhelming retaliation—attack us, and we will respond by laying waste to your cities. For that threat to work, one’s own nuclear assets must be able to survive the enemy’s initial attack. France certainly has that capability, since most of its warheads are deployed on submarines, which are notoriously hard to detect and destroy. But what if the aggressor used low-yield tactical weapons, and what if the target lay on the far edges of the Franco-British nuclear umbrella? Would France and the United Kingdom, which lack tactical nuclear warheads of their own, be willing to use their high-yield strategic arsenal in response—and risk total annihilation if the enemy responded in kind?

The answer might be no, and the obvious implication is that France and the United Kingdom cannot currently offer their allies the kind of extended deterrent afforded by the U.S. nuclear umbrella. Getting there would require substantial investments in their respective arsenals to increase the number of strategic warheads, acquire tactical ones, and deploy them in a way that they could survive a first strike by an opponent. Given their budgetary constraints, it is unlikely that Paris and London could shoulder the burden of these investments on their own. Instead, most of the bill would have to be footed by the nuclear umbrella’s future beneficiaries - that is, other European allies.

France and the United Kingdom have consistently maintained that any decision to use nuclear weapons is a matter of national sovereignty. They would thus need to issue credible assurances of protection to any third-party investors. Europe’s limited geographic scale and deep economic integration make such assurances more plausible than transatlantic pledges of protection by the United States. Nonetheless, a credible deterrent would require further arrangements. Nuclear-sharing agreements between the United States and its allies offer a useful template: under these pacts, the U.S. military deploys nuclear weapons to a number of allied states, and the host countries then provide some components of the necessary delivery systems, such as carrier aircraft and pilots. But Washington retains the sole authority to order a nuclear launch. The credibility of Paris’s and London’s assurances could also be enhanced by the creation of a consultation mechanism similar to NATO’s Nuclear Planning Group, which discusses nuclear issues and reviews member states’ policies but of which France is not a member.

Still, another major weak spot would remain. Judging by the outcomes of recent elections in France and the United Kingdom, one cannot rule out the rise, in both countries, of right-wing populist governments whose geopolitical instincts would lead them to pursue a France-only or United Kingdom–only nuclear policy. In other words, a Franco-British nuclear umbrella might one day snap shut for the same reasons the

 

Deterrence By Committee

To mitigate the uncertainties that would complicate the Franco-British option, European leaders could set their sights on a more ambitious one: a collective, pan-European nuclear deterrent. During the Cold War, officials in the Kennedy administration considered a version of this arrangement: a multinational fleet of ships and submarines armed with American nuclear weapons but operated, owned, and controlled entirely by European NATO allies. The fleet would have carried enough warheads to destroy anywhere from 25 to 100 Soviet cities. But British opposition to the plan, as well as disagreements among other allies on how to implement and fund it, caused it to founder.

A modern version of this proposal could place French and British nuclear weapons under the control of the European Union or a new body. This plan would solve the political problem posed by the Franco-British option, since it would be less vulnerable to a change of heart on the part of France or the United Kingdom. In the short term, the technical shortcomings of the Franco-British option would remain, since the collective deterrent would rely on the two countries’ arsenals. But Europe’s nonnuclear powers would have a much stronger incentive to share the financial burden of modernizing and expanding the French and British nuclear stockpile than they would have under the first option, since they would be investing in a jointly controlled arsenal rather than in weapons wholly controlled by others.

Joint control would represent the arrangement’s greatest strength for most of the continent, but it would be a nonstarter for Paris and London. Neither government would want to hand over its national arsenal to a European body and give up the final say on the weapons’ use. Even if a multilateral nuclear force provided enhanced capabilities and thus a higher level of deterrence - whose benefits would also redound to the French and the British - the question of who held the ultimate launch authority would likely outweigh any other considerations.

Joint control raises other thorny issues, too. If only a single member state of the multilateral force suffered a nuclear attack, would the others really prove willing to respond? If they didn’t, would that give the attacked country the right to conduct a unilateral retaliatory strike, using nuclear weapons stationed on its territory as part of the multilateral force? Would a nuclear strike require unanimity among member states, or would a majority suffice? In either case, decision-making would require more time than is available during a potential nuclear conflict. To avoid delays, the launch authority could be delegated to a supranational body. But that body would not have enough democratic legitimacy to make life-or-death decisions for hundreds of millions of people. Until European nations have reached a level of integration that would allow a directly elected European government to make such a decision, option two would fail the credibility test.

 

Who’s Next?

What remains is undoubtedly the most controversial and far-reaching option: instead of relying on or investing in the existing French and British arsenals, other European countries could build nuclear weapons of their own. If these states accumulated arsenals comparable in size to those of France and the United Kingdom, Europe’s collective capabilities would extend beyond deterrence by punishment. Rather than merely threatening retaliation in the wake of an attack, European states would be able to engage in “deterrence by denial” - that is, to make it difficult or even impossible for an adversary to carry out a devastating strike in the first place.

Several major European powers, chief among them Germany and Poland, could theoretically acquire the technological capabilities and allocate the financial resources necessary to amass enough enriched uranium and ultimately develop nuclear weapons. But doing so would still take time - certainly enough time for a potential nuclear-armed aggressor such as Russia to carry out a preemptive conventional strike on enrichment sites and other development facilities. Before Russia’s full-scale invasion of Ukraine, such a strike would have been unthinkable. Nowadays, hardly anything can be excluded.

To mitigate that risk, France and the United Kingdom could “lend out” some of their nuclear weapons temporarily. The incentive for Paris and London to go along with this plan and support the nuclear ambitions of their allies would be to achieve strength in numbers: even without joint control, multiple European nuclear powers could establish a greater level of deterrence than France and the United Kingdom can establish for themselves today. The United States, for its part, would at long last be relieved of the burden of protecting Europe, freeing resources for alternative uses. But if the benefits are of historic proportions, so, too, are the potential costs - especially the raised risk of provoking a conflict with Russia.

Turkish and Spanish soldiers during NATO training in Barbate, Spain, March 2025

In practice, there is no obvious contender for the position of Europe’s third nuclear power. So far, only Poland seems to be weighing the option in earnest. “Poland must pursue the most advanced capabilities, including nuclear and modern unconventional weapons,” Tusk, the country’s prime minister, told Polish parliamentarians in March. “This is a serious race - a race for security, not for war.”

The debate in Germany, meanwhile, is complicated by historical, political, cultural, and strategic considerations. Despite decades of reconciliation, integration, and democratic stability, the first half of the twentieth century - and Germany’s role in It - still weighs heavily on European minds. A nuclear-armed Germany would entail a significant rebalancing of power in Europe and trigger deep concern in neighboring capitals. That is to say nothing of German society’s own wariness. Its pacifist and antinuclear leanings run deep, as do its aversion to risk and its reservations about taking on international military responsibilities. Even the civilian use of nuclear energy has been phased out, with the last reactors shut down in April 2023. These societal and political instincts are hardly compatible with the role of a nuclear power.

The legal constraints on Germany are significant, too. As a party to the Nuclear Nonproliferation Treaty, the country has renounced the production and possession of nuclear weapons. The same commitment is enshrined in Article 3(1) of the Two Plus Four Treaty, the 1990 agreement that provided the legal foundation for the post–Cold War reunification of East and West Germany. The Two Plus Four Treaty, in particular, is a daunting legal obstacle, as a violation of one of its central elements could put the validity of the whole document into question. That, in turn, would cause major concerns among its signatories and among Germany’s immediate neighbors.

To be sure, recent events have already undercut the treaty’s political basis. Russia’s full-scale invasion of Ukraine and the possibility of a U.S. withdrawal from Europe each threaten the very achievement that the accord was meant to secure, namely the full sovereignty of a reunified Germany. These unsettling changes could be reason enough for a joint decision by Germany, the United Kingdom, and the United States to override Article 3(1). Nevertheless, any move by Germany toward the acquisition of nuclear weapons would be imaginable only in close consultation and concert with other European states, first and foremost Poland, where a nuclear-armed Germany would cause the most apprehension.

 

All of the Above

For the time being, none of the three options easily pass the credibility test. A French and British nuclear umbrella would lack the necessary capabilities, and its beneficiaries would likely doubt its reliability in times of crisis. A pan-European nuclear deterrent appears even less feasible. It would transfer an existential political decision to an entity with only indirect democratic legitimacy. Doing so would amount to a serious challenge to European democratic norms at a time when they are already under assault by illiberal forces.

Nuclear proliferation in Europe might provide effective and credible deterrence. But it would carry legal and political risks that, for the time being, are too great for European leaders to countenance. It could also set off a wave of nuclear proliferation outside Europe, including in states that Western governments consider hostile.

Then again, even if Europe stays put, there is no knowing if nonproliferation will hold in other parts of the world. If anything, current trends suggest that the first place it will buckle is East Asia. If the Trump administration continues to create a sense of uncertainty about the U.S. security guarantee to South Korea, for example, leaders in Seoul could reach a breaking point. As things stand, South Korea faces three politically hostile nuclear powers - North Korea, China, and Russia - in its immediate neighborhood. South Korean defense strategists have pointed out that this situation would become untenable if their country’s only nuclear ally, the United States, were to withdraw. A nuclear-armed South Korea would, in turn, encourage Japan to pursue the same course.

Nuclear proliferation in East Asia would also alter the terms of the debate in Europe, where it might be viewed as a shift more real and definitive than Trump’s threats alone. It is a sobering scenario: European leaders, faced with nothing but bad options, may prove incapable of breaking their nuclear impasse unless someone else takes the plunge first. Europe’s safest bet, until then, is to at least prepare for all contingencies.

 

 

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