The year is 2030. Seismic monitors have just detected an unforeseen underground atomic explosion, signaling that yet another country has joined the growing club of nuclear-armed states. There are now 20 such countries, more than double the number in 2021. To the surprise of many, the proliferation has come not from rogue states bent on committing nuclear blackmail but from a group of countries usually seen as cautious and rule abiding: U.S. allies. Even though they had forsworn acquiring nuclear capabilities decades earlier when they signed the Nuclear Nonproliferation Treaty (NPT), these allies changed their minds and withdrew from the agreement, a move that triggered yet more defections as nations across the world raced to acquire the bomb. And so the number of nuclear decision-makers multiplied, raising the odds of a terrifying possibility: that one of these powerful weapons might go off.

Far-fetched? Perhaps, but this scenario is more plausible now than many think. Although the threat of nuclear proliferation in recent decades has been concentrated in the Middle East and Asia, that wasn’t always the case. In the 1960s, Washington worried about its Asian and European allies going nuclear. U.S. intelligence officials projected that by the mid-1970s, there could be 10 to 15 nuclear powers in the world, including Australia, Germany, Italy, Japan, South Korea, and Turkey. The NPT was designed to prevent this possibility, and since it was signed, in 1968, only four countries (India, Israel, Pakistan, and North Korea) have acquired and retained operational nuclear forces. This success was due in large part to the United States’ concerted efforts to extend its nuclear umbrella to allied territory. Reassured that they would be protected from nuclear attack and intimidation, U.S. allies in Asia and Europe decided not to develop their own nuclear capabilities.

But now they may be rethinking that decision. In both Asia and Europe, U.S. allies face a growing military threat from nuclear-armed powers, as China and Russia each become more aggressive and modernize their nuclear forces. And in the United States, allies see a government that has walked away from long-standing arms control agreements and a population that no longer seems committed to global engagement. All of this has left U.S. allies wondering whether they can still rely on Washington for their defense and security—or whether it might be time to think about getting the bomb.

In his inaugural address, President Joe Biden pledged, “We will repair our alliances.” But after the Trump administration did so much to sow mistrust, it will take more than words to reassure allies of the United States’ commitments and erase any thoughts of joining the nuclear club. It will also take active steps to bolster confidence in the United States’ nuclear guarantee, reinvigorated defense cooperation with allies, and a complete rethinking of arms control. This is a big agenda. But it is doable.


Most of the discussions in allied capitals about the U.S. nuclear umbrella have played out beyond public view, but signs of disquiet are beginning to emerge. In Germany, doubts about the United States’ reliability have arisen within official circles, and a growing chorus of voices outside government has suggested possible alternatives to the U.S. nuclear guarantee. Some have proposed relying instead on a European nuclear umbrella composed of some combination of French and British capabilities, perhaps supported financially by Germany and other nonnuclear European countries. France, for its part, has invited fellow European states to engage in a “strategic dialogue” on its nuclear deterrent and possibly participate in nuclear exercises.

In Poland, there have been calls to bolster Europe’s nuclear deterrence, with Jaroslaw Kaczynski, the leader of the country’s governing party, welcoming the idea of the EU as a nuclear power with an arsenal equal to that of Russia’s. Turkey, too, has shown an interest in the bomb, with its president, Recep Tayyip Erdogan, suggesting that he is open to the possibility of acquiring it. “Several countries have missiles with nuclear warheads, not one or two. But we can’t have them,” he said. “This I cannot accept.”

In both Asia and Europe, U.S. allies face a growing military threat from nuclear-armed powers.

Similar sentiments are emerging in Asia. Japan, the only country in history to have suffered a nuclear attack, is concerned about the continued reliability of the U.S. nuclear umbrella, especially as its nuclear-armed neighbors become more aggressive. Doubts about U.S. reliability are nothing new in Japan: in the 1970s, the country delayed ratifying the NPT for more than five years, worried that the treaty would enshrine its nuclear inferiority and that the U.S. umbrella might prove insufficient to ensure Japan’s security. Today, such sentiment has been compounded by China’s newfound assertiveness and North Korea’s nuclear advances. And although Japanese officials are not openly raising the possibility that their country will acquire a nuclear arsenal of its own, Japan continues to maintain the material and know-how to do so rapidly should it decide to.

South Korea has also been questioning its lack of a nuclear arsenal. North Korea first tested a nuclear weapon in 2006, and in the years since, it has built dozens of weapons and hundreds of missiles, some of which could reach the continental United States. Adding to South Korea’s feelings of insecurity, in 2019, the Trump administration canceled joint military exercises with the country and demanded that it quintuple the amount it pays for the privilege of keeping tens of thousands of U.S. troops on the Korean Peninsula. Although few South Koreans have advocated a national nuclear deterrent, more and more of them want greater reassurance from the United States. Many have called for Washington to reintroduce the tactical nuclear weapons—short-range and low-yield—that it withdrew after the Cold War.

In Australia, finally, growing concern about China has led to what the Australian government has called “the most consequential strategic realignment” of its defense policy since World War II: a clear focus on defending its national security in an Indo-Pacific region marked by great-power competition and a rising chance of conflict. Although Australia is not yet rethinking its nuclear abstinence, it has decided to acquire long-range strike capabilities to enhance the credibility of its defense and deterrence posture. If doubts about U.S. reliability were to prove more than a temporary phenomenon, the same logic could lead to a renewed debate about Australia’s nonnuclear policy.


Reassuring allies starts with a return to fundamentals: the Biden administration must unequivocally reaffirm the cornerstones of U.S. security commitments. That means affirming the United States’ treaty commitments to collective defense, reversing the Trump administration’s decision to remove U.S. troops from Germany and elsewhere, and negotiating long-term cost-sharing arrangements with the countries that host U.S. troops in Asia and Europe.

To erase doubts about the U.S. umbrella, the Biden administration should raise the salience of nuclear issues with allies. It should bring NATO and Asian allies into the nuclear planning process from the outset, closely consulting them as the administration conducts its next Nuclear Posture Review. The administration should plan more exercises with U.S. allies that include a nuclear dimension and regularly involve allied political leaders in them. Finally, it should seek to bolster the defense and deterrence capabilities of its alliances in Asia and Europe. That may entail increasing the number of U.S. troops in both regions or, at the very least, pledging to maintain their current levels. It may also entail deploying additional missile defense capabilities and reviewing the U.S. nuclear posture in both regions to ensure that existing capabilities are enough to maintain the credibility of the U.S. nuclear umbrella. Whatever the decisions, they should be taken only in close consultation with, and at the invitation of, U.S. allies.

Allies will have to do their part. Europe, as German Chancellor Angela Merkel has said, must “take on more responsibility, both in military and diplomatic terms.” But it should do so by building up real military capacity—improved warfighting capabilities, enhanced readiness—not just more procedures or headquarters. Europe will also need to build up the nuclear dimension of its defense efforts. European allies that currently participate in NATO nuclear missions by deploying aircraft and hosting U.S. weapons should retain and modernize these forces.

Western Europe’s two nuclear powers, France and the United Kingdom, should not only deepen their long-standing nuclear cooperation but also offer to extend their nuclear deterrents to their European allies. The result would be a European nuclear umbrella, something that would complement rather than replace the U.S. nuclear guarantee yet still strengthen NATO and bolster European security. Indeed, that is the point of greater European capabilities, and the United States should make clear that it welcomes any efforts to strengthen defense cooperation within Europe. The region’s ability to act autonomously poses no threat to the United States or NATO; to the contrary, it makes Europe a stronger military partner.

Arms control must move beyond the U.S.-Russian framework that has dominated for decades.

Restoring confidence among U.S. allies in Asia will be trickier, because the region lacks its own version of NATO and relies instead on bilateral security arrangements. To compensate, Washington should encourage greater cooperation among its Asian allies and reestablish trilateral security cooperation with Japan and South Korea, which was halted in recent years because of disputes between the two Asian powers. Washington should also establish an Asian equivalent to NATO’s Nuclear Planning Group, a body that would bring Australia, Japan, and South Korea into the U.S. nuclear planning process and offer them a platform for discussing regional deterrence. Finally, the United States and the three other countries in the Asia Quadrilateral Security Dialogue (Australia, India, and Japan) may need to consider eventually including South Korea in the group if Seoul expresses interest in joining.

The biggest nuclear unknown in the coming decade concerns China’s arsenal, which, although shrouded in secrecy, is believed to be undergoing rapid modernization and could double in size within a few years. The United States and its allies have a powerful incentive to penetrate China’s nuclear opacity and get greater insight into its capabilities. Arms control agreements can play a role in this effort, providing greater transparency about capabilities, an exchange of views on intentions, and stability in the overall nuclear relationship.

Indeed, the United States needs to overhaul its approach to arms control globally. Biden took a wise first step when he agreed to extend the New START treaty with Russia, which covers only long-range strategic weapons; the next step should be a new bilateral agreement that would seek to cover all U.S. and Russian nuclear warheads, including those in storage, as well as novel nuclear delivery systems, such as hypersonic weapons.

That said, arms control must move beyond the U.S.-Russian framework that has dominated for decades. A logical grouping for expanded discussions would be the five permanent members of the UN Security Council—China, France, Russia, the United Kingdom, and the United States. These five countries should start a dialogue that addresses nuclear issues, and over time, they could negotiate measures that would pull back the curtain on their arsenals, convince one another of the defensive nature of those arsenals, and open up the possibility of mutual limitations. As a first step, the United States and Russia could invite the other three members to observe the inspections that Washington and Moscow conduct as part of their existing arms control obligations, thus demonstrating the value of transparency without revealing critical secrets about weapons designs. Subsequently, all five countries could agree to exchange information about their nuclear capabilities, notify each other of forthcoming missile and other tests, and take other steps to enhance transparency. Eventually, each country could commit to limiting its nuclear forces to the lowest possible level.


For more than 50 years, the United States’ alliances have helped stop the spread of nuclear weapons. But faced with worsening regional threats and growing uncertainty about U.S. staying power, U.S. allies are beginning to reassess their security arrangements—including their nuclear dimensions.

Biden has made rebuilding U.S. alliances a fundamental priority from the moment he took office. The president was right to reaffirm the U.S. commitment to NATO in a call with the alliance’s secretary-general and key European allies, and he was right to do the same regarding Australia, Japan, and South Korea in calls to those countries’ leaders.

Now, however, comes the hard work of transforming relationships in more fundamental ways—bolstering deterrence and defense capabilities all around, bringing Asian and European allies into the U.S. nuclear planning process, and broadening arms control efforts beyond Russia. This is hardly an impossible agenda, but it could hardly be more urgent. At stake is nothing less than a decades-long success: preventing the spread of the world’s deadliest weapons.  

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