Do Friends Let Friends Go Nuclear?

For the past few decades, the United States and its partners have wrestled with how to deal with a hostile country’s decision to acquire nuclear weapons. Nuclear programs in Libya, North Korea, and Iran were condemned by Washington and its allies as threats to peace and to the global nonproliferation regime. The United States and others adopted a range of policies, both carrots and sticks, to prevent “rogue” nations from going nuclear.

Today, the United States faces a different proliferation challenge. U.S. allies and members in good standing of the Nuclear Non-Proliferation Treaty (NPT)—such as Germany, Poland, and South Korea—are expressing fears about growing regional threats, doubting the reliability of U.S. nuclear umbrellas, and debating whether they need nuclear weapons to bolster their security. How should the United States and other countries respond?

Anxiety on the Peninsula

In South Korea, North Korea’s development of intercontinental missile capabilities has fueled fears about the credibility of the U.S. nuclear umbrella. Previously, if North Korea used nuclear weapons against the south in a war, the United States could promise to retaliate without fear of American cities being hit. Today, however, U.S. cities would be in North Korea’s crosshairs. Many South Koreans doubt that a U.S. leader would decide to strike if it would put U.S. cities and citizens at risk.

As a result, South Korea’s long-dormant debate about an independent nuclear arsenal has resurfaced. Many officials and foreign policy elites express support for developing weapons, and polls show a majority of the public—around 70 percent—also approves. Other options being debated are the return of U.S. tactical nuclear weapons to the peninsula or a nuclear sharing agreement with the United States.

During the 2022 Washington Summit between the two countries, the Biden administration sought to reassure South Korea of the credibility of the U.S. deterrent. The administration pledged to consult Seoul in nuclear planning for the peninsula and sent a nuclear-capable submarine for a port visit to Busan. Since the summit, however, “South Korean public confidence in the credibility of U.S. nuclear assurances has not increased,” reports the Asan Institute in Seoul. “In fact, survey results show that it has actually decreased.” The debate is thus far from resolved—and may intensify if Donald Trump is elected in November. After all, statements by Trump in his 2016 presidential campaign and while in office alarmed South Koreans that the United States might draw down its military forces on the peninsula—or end the alliance altogether.

South Korea is an NPT member, but the treaty’s Article 10 allows for members to withdraw if “extraordinary events, related to the subject matter of this [t]reaty, have jeopardized the supreme interests of its country.” When North Korea withdrew from the NPT in 2003, it also cited Article 10, but many NPT members rejected its argument. North Korea’s nuclear program has since faced nine UN Security Council sanctions resolutions. Many South Koreans worry that they would face similar opprobrium and sanctions if they followed suit.

Rising Threat Perception in Europe

South Korea isn’t alone in its doubts about the U.S. nuclear umbrella. Russia’s invasion of Ukraine has significantly elevated threat perception in Europe, and recent trends in the United States also worry European leaders. They see a large and influential faction of Republicans in Congress rejecting aid to Ukraine and are alarmed by the prospect of a second Trump presidency, given his statements criticizing NATO countries’ “delinquency.” More broadly, European leaders perceive that America’s longtime bipartisan globalist consensus is dissipating, as the New York Times’s Peter Baker writes, “under the weight of globalization, the wars in Iraq and Afghanistan, the Great Recession of 2008-09 and Mr. Trump’s relentless assault on international institutions and agreements.”

As a result of these trends, European analysts are increasingly debating what a future European nuclear posture might look like absent the United States. France’s president startled many observers last week when he suggested that French nuclear weapons could provide an umbrella for the broader European Union. Emmanuel Macron said, “I’m in favor of opening this debate, which must therefore include missile defense, long-range weapons and nuclear weapons for those who have them or who have American nuclear weapons on their soil.” The French president commented, “Let’s put everything on the table and see what really protects us in a credible way.”

Sharing a border with Ukraine and hosting millions of war refugees, Poland feels the threat of Russian aggression keenly. Poland’s prime minister announced in 2023 his country’s desire to host NATO nuclear weapons. “Due to the fact that Russia intends to site tactical nuclear weapons in Belarus,” said Mateusz Morawiecki, “we are all the more asking the whole of NATO about taking part in the nuclear sharing program.” Poland’s defense minister had made a similar statement in the wake of Russia’s 2014 annexation of Crimea.

NATO’s nuclear sharing program began in the 1960s. Members of the program include Belgium, Germany, Italy, the Netherlands, and Turkey; Poland would be the sixth member. Members currently host about 150 U.S. B61 nuclear gravity bombs—bombs that remain under U.S. control. This allows both the United States and host countries to remain in good standing with the NPT, which forbids the United States from transferring nuclear weapons and forbids the other countries from receiving them. Host countries’ military forces train for nuclear missions and maintain the aircraft that would deliver the weapons. The United States maintains the legality of NATO nuclear sharing under the NPT because the program does “not involve any transfer of nuclear weapons or control over them unless and until a decision were made to go to war, at which time the treaty would no longer be controlling.” (NATO also asserts that its nuclear sharing is legal because the program predates the NPT.)

Similar to today, NATO nuclear sharing was created to reassure U.S. allies about the credibility of the American nuclear umbrella. Namely, after the Soviet Union developed the capability to strike the United States with nuclear weapons in the 1960s, NATO countries worried whether the United States would ever retaliate on their behalf. For decades, NATO nuclear sharing has reassured U.S. allies. It may prove a solution to Poland’s current fears.

In Germany, however, many people wonder whether NATO nuclear sharing is enough. During the Trump administration, the president’s criticism of NATO initiated a German debate about a previously taboo topic. The newspaper Welt am Sonntag queried, “Do we need the bomb?” At the time, Maximilian Terhalle, a German academic based in the United Kingdom, wrote that Trump left Germany pondering “whether to continue relying on a United States that is now committed to signaling its unreliability or to begin pursuing its own nuclear deterrent—either on its own or as part of a new European security structure.”

Trump’s political resurgence has reinvigorated Germany’s nuclear debate. “Atomic hawks,” writes Matthew Karnitschnig, say “Germany must go nuclear! With Russia inching forward in Ukraine, the U.S. threatening to flake out as an ally, Germany should waste no time in pulling together a nuclear arsenal.” But Karnitschnig and others note that Germany has a long-standing anti-nuclear movement with deep connections to German politics. The move to acquire nuclear weapons would involve a wrenching debate, one requiring Germany’s perception of the threat from Russia—and doubts about the United States—to be severe.

Today’s New Proliferation Challenge

Currently, Brussels, London, and Washington maintain a firm nonproliferation stance. At the Group of Seven’s Hiroshima summit in 2023, the group issued a statement renewing its “commitment to achieving a world without nuclear weapons with undiminished security for all.” It also reiterated that the “overall decline in global nuclear arsenals achieved since the end of the Cold War must continue and not be reversed” and that “[t]he Treaty on the Non-proliferation of Nuclear Weapons (NPT) must be upheld as the cornerstone of the global nuclear non-proliferation regime.” 

But how should the United States, the European Union, the United Kingdom, and others react when friendly countries—liberal democracies and law-abiding NPT members—argue that they perceive a security threat so dire they must abandon their nonproliferation stance? Given America’s long-standing commitment to nuclear nonproliferation, the natural inclination among U.S. leaders may be to reiterate that America values its alliances and to dissuade and pressure its friends from going nuclear. But if countries ultimately decide to take the step, a lack of U.S. empathy could jeopardize alliance relationships. After all, other countries remember that the United States accepted the spread of nuclear weapons to Britain, France, and Israel—and so would wonder why Washington cannot show similar understanding to another friend that believes its existential security is at risk.

To address today’s proliferation challenges, the first move—as shown by the Biden administration’s policies toward South Korea—is to listen to allies’ concerns. Washington might take steps, as it did after the Washington Summit, to reassure the ally of the continued credibility of the nuclear umbrella. In some cases, conventional military solutions may be possible to bolster deterrence. It’s quite possible that today’s reluctant proliferators—loath to undermine the NPT, facing domestic political resistance, fearful of sanctions or nuclear cascades—could be reassured by such policies. But if they prove insufficient, the United States and its partners can discuss options along a “nuclear continuum.” As Daryl Press and I have written, rather than facing a binary decision to “go nuclear” or not, countries have a range of options. Poland’s interest in nuclear sharing is an example of a step, short of nuclear acquisition, that a country might take to increase its security.

Because countries vary significantly in their levels of threat perception, anxiety about the U.S. security commitment, and public support for nuclear weapons, solutions will vary by case. But as anxieties among U.S. allies grow, it is increasingly important for leaders in the United States and elsewhere to think about what those solutions might be.