Over the last year, two key U.S. security partners openly alluded to acquiring atomic weapons in apparent attempts to compel concessions from the United States. In January 2023, South Korean President Yoon Suk-yeol floated the notion that Seoul might need its own nuclear force to counter North Korea’s growing strategic arsenal. But Yoon’s remarks seemed more designed to influence alliance negotiations with Washington than to express a clear commitment to proliferate: he underscored that Seoul would continue to rely on U.S. extended deterrent commitments “for now.”
Similarly, in September, Saudi Crown Prince Mohammed bin Salman repeated a well-worn proliferation threat, telling Fox News that if Iran acquired the bomb, Saudi Arabia would “have to get one” as well. But then he added that the kingdom did not want to see such an outcome unfold in the Middle East. While the crown prince’s remarks may have been primarily aimed at leaders in Tehran, they happened to coincide with an effort to extract concessions from Washington—including a formal defense pact—during diplomacy over normalization with Israel.
Absent clear technical indications of a nuclear weapons effort, the nuclear musings from South Korea and Saudi Arabia seem to be about gaining greater leverage over the United States. Dialing up the prospect of proliferation in this manner sent a clear message: unless Washington yields to demands for greater defense support, Seoul or Riyadh will have no choice but to reconsider their respective nuclear weapons options. The United States therefore finds itself facing a dilemma between giving in to such demands or suffering nonproliferation failures.
Toying with atomic weapons aspirations is not a new approach to increasing pressure on a superpower; in fact, it is an enduring feature of the nuclear age. A small but diverse club of countries have periodically played with building the bomb as a diplomatic lever against superpowers who oppose proliferation, most prominently the United States. Some early pioneers, such as West Germany and Japan, used investments in nuclear energy technology in the 1960s to pressure Washington into providing stronger security commitments or military assistance during the Cold War. Others, notably North Korea and Iran, adopted this unique form of coercive diplomacy after they were caught in secret pursuit of nuclear weapons.
Yet leveraging nuclear latency—the technical capacity to build the bomb—only tends to work in very specific circumstances. As I find in a new book on the topic, Leveraging Latency: How the Weak Compel the Strong with Nuclear Technology (Oxford University Press, 2023), some allies and adversaries have been effective in using the mere threat of proliferation to wrest concessions from the United States. But these success cases stand out against a longer track record of failure. Many other leaders have been unable to bring home concrete benefits and have instead experienced costly international blowback.
Will the recent efforts of South Korea and Saudi Arabia be successful? How should Washington manage the nuclear signals coming out of Seoul and Riyadh? Answering these questions requires examining why the United States is so sensitive to proliferation, how smaller states exploit this pressure point by threatening to build the bomb, and when the approach is most likely to work.
Why Is Proliferation a Pressure Point for the United States?
Using nuclear technology as a coercive instrument adheres to a sound strategic logic. Superpowers, notably the United States, face strong incentives to keep adversaries and even close allies from acquiring the bomb. This is because proliferation promises to neutralize many of the advantages nuclear powers enjoy on the world stage.
Atomic weapons are great equalizers among nations. If a small state builds even a rudimentary nuclear force, it can undercut a larger state’s ability to bully or overthrow them by force. This point is rather obvious to the United States, as illustrated by its fixation on keeping nuclear weapons out of the hands of so-called “rogue states” and adversaries that seek to blunt American might.
Regarding proliferation among select allies or partners, however, the United States has sometimes seen it as useful in certain situations. For example, U.S. president Dwight Eisenhower believed that West Germany’s looming potential to build the bomb in the 1950s helped to keep the Soviet Union in check during the early Cold War. And even today, proliferation among allies may be seen in a similar way vis-à-vis countering China. But nearly all U.S. leaders and officials view ally proliferation as deeply dangerous for three reasons.
First, allowing allies and partners to acquire nuclear weapons risks entrapping the United States in unwanted conflict. Under the administration of president John F. Kennedy, U.S. officials increasingly feared that if West Germany acquired the bomb, Bonn would become emboldened to push for reunification with East Germany, thereby dragging Washington into a major crisis with the Soviets. Similar concerns drove the United States to oppose efforts by South Korea and Taiwan to develop fissile material production technologies in the 1970s.
Second, ally proliferation bedevils escalation management. Smaller allies and partners may lack the resources necessary to secure their new nuclear arsenals against a crippling first strike from a larger adversary. And this could make it more difficult for the United States to manage the early stages of a crisis involving an ally and a larger nuclear-armed adversary. In the case of West Germany, for instance, the fear was that a hypothetical German nuclear arsenal would be small, vulnerable, and outside of U.S. control and that Bonn would therefore feel pressure to employ nuclear weapons at the outset—before the much larger and more sophisticated Soviet force had a chance to neutralize the arsenal. U.S. officials subsequently opposed ally proliferation elsewhere for precisely this reason.
Third, selective proliferation is likely to drive general proliferation. Fear of entrapment and preemption need not hang over every alliance or partnership, but it is exceedingly difficult to manage the spread of nuclear weapons to some allies but not others. Nuclear domino theory—the belief that one state acquiring the bomb would lead others to follow suit—became a central tenet in U.S. national security strategy after China’s first nuclear test in 1964 led a handful of states to consider and even pursue nuclear weapons. As a result, U.S. officials strengthened their efforts to stop even allies and partners from igniting such reactive proliferation cascades. In particular, Washington worked closely with Moscow to craft the core pillars of the 1968 Nuclear Nonproliferation Treaty (NPT) and then pressured allies into joining this key institution, thereby setting the multilateral foundation of the global nonproliferation regime.
Taken together, these concerns have formed the backbone of near totalAmerican opposition to the spread of nuclear weapons over the last seven decades. However, during this period, some states have preyed upon Washington’s fear of future proliferation. By carefully moving closer to the bomb, or perhaps just threatening to do so, these countries attempted to ratchet up pressure on the United States. In response, U.S. administrations have periodically faced complying with various demands from friends and enemies to avoid living under this nuclear sword of Damocles.
How Do Countries Leverage Nuclear Latency?
Leveraging nuclear latency—that is, atomic bomb making capacity—requires states to make both their threats and assurances credible. On the one hand, they must first threaten to build the bomb unless the United States yields to its demands. But Washington may have good reason to suspect that some potential proliferators, especially allies and partners, are exaggerating their weapon ambitions as a negotiation ploy. High-ranking Saudi officials, for example, have been making periodic threats to match Iran’s nuclear program and build an advanced nuclear energy enterprise for over a decade. Yet the kingdom has taken few concrete steps toward developing such capabilities. Exaggeration is alluring here because proliferation involves significant costs and risks. If a state can compel concessions from the United States merely by feigning interest in the bomb, then it has an incentive to drum up such concerns. As a result, leaders must convince Washington that they will follow through with the threat to acquire atomic weapons.
On the other hand, potential proliferators need to commit themselves to nuclear forbearance if the United States complies with their demands. Assurances play a critical role in this type of coercion, Thomas Schelling reminds us, because the threat of punishment must be “stopped or reversed when the enemy complies, or else there is no inducement.” Yet making the promise of forbearance credible is no easy task. U.S. officials may doubt the nonproliferation bona fides of even its allies for good reason. Some states could offer up false promises of nuclear restraint as a ruse to buy time and alleviate pressure—only to resume the pursuit of weapons later. Taiwan, for example, briefly resumed the clandestine construction of fissile material production facilities in the late 1980s, despite acquiescing to U.S. demands to give up its quest for the bomb in the 1970s.
Other countries may genuinely want to trade away their weapons ambitions, but their nonproliferation incentives can erode as domestic or geopolitical conditions change over time. The case of Japan’s budding civil nuclear energy program in the mid-1960s provides a prime illustration. By 1965, U.S. officials concluded that the Japanese leadership was unlikely to use investments in plutonium reprocessing to build the bomb in the near term. But because Washington worried that Tokyo might reconsider its nuclear options down the road, particularly if the alliance weakened or China posed a more severe security threat, the United States wanted Japan to join the vanguard of what would soon become the NPT movement. As a negotiation tactic, Japanese leaders carefully cultivated this U.S. concern with a chatter campaign hinting that they wanted to keep the nuclear door ajar. They eventually joined the NPT, but only after Washington had acceded to demands for stronger security commitments and the territorial reversion of Okinawa. As Japan demonstrates, allies must commit themselves to nuclear restraint after playing the proliferation card so that Washington is compelled to deliver the desired benefits.
So, what tactics enable leaders to make both threats and assurances more credible? On the threat side of the coin, the most explicit tactics involve mobilizing or protecting nuclear enterprises, such as Iran’s past efforts to ramp up production at hardened nuclear fuel enrichment plants or North Korea’s plutonium reprocessing campaigns in the 1990s and early 2000s. Such steps vividly demonstrate one’s capacity and resolve to produce the most crucial ingredient in an atomic weapon: the fissile material that fuels the explosive core. This highly enriched uranium or plutonium is essential to building the bomb and therefore helps underwrite the technical threat of proliferation. The intensive financial outlays and security risks required to develop fissile material plants, and harden them from attack, are extremely costly and thus screen out opportunistic bluffers.
Mobilizing nuclear assets need not involve a blatant march toward the bomb, however. Leaders can also use civil nuclear energy infrastructure built in plain sight to enhance proliferation threat credibility. The dual-use nature of the technology means that these ostensibly peaceful programs can still be helpful in building the bomb down the road.
In 1963, West Germany’s growing nuclear energy program enabled leaders to leverage proliferation pressure on Washington to shore up its security commitments, specifically by granting some degree of German participation in NATO nuclear-sharing arrangements. Nuclear industry stakeholders in West Germany were building plutonium reprocessing capabilities with a view toward reaping economic benefits from the back end of the nuclear fuel cycle. But this ability to produce fissile material triggered over-the-horizon concerns in Washington about German proliferation. Once reprocessing operations began, Bonn would quickly possess enough plutonium for a small nuclear arsenal.
Over the next three years, West German leaders appeared to take advantage of this civilian-led growth in the nuclear program, using it to make their implicit proliferation threats more credible. Although Washington rebuffed demands to share control over NATO nuclear forces with Bonn, West Germany managed to wrangle a permanent seat on NATO’s Nuclear Planning Group—a consultative venue where allies could share information and coordinate nuclear plans.
Finally, the arena of domestic politics provides leaders with several methods for underwriting proliferation threats. It is hard and expensive to build nuclear assets. The technology itself may be old, but spinning up large and intricate infrastructure is no small feat. Empowering scientists, industrial stakeholders, and other elites with resources commits the state to move forward with nuclear projects. Cultivating broad public support for these endeavors also increases the political costs of giving up on nuclear ambitions.
In the early 1960s, Tokyo vested elites with the funding and political autonomy necessary to build Japan’s civil nuclear program. The public also came around to support atomic energy after concerted outreach efforts from government and industry. The state’s strong commitments propelled Japan toward its fissile material production goals, albeit for peaceful purposes. But because these technology investments were backed by important constituencies, Japanese leaders faced stronger incentives not to back down in subsequent negotiations (1964–1970) to shore up U.S. defense commitments and wrest back territorial control of the Western Pacific islands from Washington—the Bonin archipelago and the Ryukyu island chain, including Okinawa.
On the assurance side on the coin, leaders must also attempt to reverse or at least neutralize these steps toward the bomb. The clearest signal of nuclear forbearance involves decreasing one’s capacity to produce fissile material and allowing intrusive inspections to verify compliance. Demobilizing this central element of atomic bomb-making capacity is often foundational to offering strong nuclear restraint commitments. A more determined proliferator using negotiations as a ruse would be unwilling to incur such delays, shine light on operations, or burn valuable investments in nuclear latency.
In a similar vein, leaders can make nuclear assets more vulnerable to attack and dependent on foreign suppliers. Nuclear programs built aboveground and enmeshed in trade agreements stand to suffer higher costs if the state decides to develop nuclear weapons. The United States, for example, sets stringent rules for how countries it assists with civil nuclear technology can use U.S. fuel and equipment. Violating these terms could result in financial devastation for a recipient nation’s civil nuclear energy sector. All else being equal, the more leaders move away from the weapons threshold, accept international inspections, and expose the nuclear program to penalties for military activities, the stronger their commitment to forgo the bomb.
Under What Conditions Does Leveraging Nuclear Latency Work?
Some states have been quite successful in employing these tactics to blend threats with assurances in negotiations with the United States. For many others, however, this type of nuclear gambit has ended in failure, with U.S. officials rebuffing demands and often pursuing more aggressive counterproliferation measures. This raises a fundamental question about the conditions required for states to successfully use nuclear latency as a tool for obtaining concessions from Washington.
States confront a trade-off when they leverage latency. On the one hand, they need enough nuclear latency to underwrite proliferation threats against far more powerful players such as the United States. When a nuclear program is in its infancy, leaders may find that they lack the technical prowess for their bargaining tactics to have real bite. Superpowers are likely to brush off proliferation threats as infeasible or cheap talk. South Korea learned this lesson in the 1970s when president Park Chung-hee attempted to gain new U.S. security commitments from presidents Richard Nixon and Gerald Ford by jump-starting a small nuclear weapons program. Park’s plan rested on a hollow technical foundation: South Korea had no capacity to produce fissile material at the time. In response, U.S. officials took quick steps to cut off Seoul’s ability to import plutonium reprocessing technology. Without this critical capability, Park lacked the leverage to push for major revisions in the U.S. alliance architecture.
On the other hand, states need to commit themselves to nuclear restraint once Washington addresses their demands. Marching toward the cusp of the bomb solves the threat credibility problem. Once a leader can call upon the nuclear enterprise to build atomic weapons on short notice, they may be in the strongest position to dial up coercive pressure. This idea has a natural allure. From 2010 to 2013, for example, Iran steadily expanded fissile material production—accumulating a sizeable stockpile of low-enriched uranium (LEU)—at observable fuel enrichment plants. In Washington, U.S. officials interpreted these moves as an effort to compel the United States into seeking a diplomatic deal before Iran acquired a fully fledged latent nuclear weapons capability.
But more atomic bomb-making capacity often increases the challenges states face with making nonproliferation assurances credible. For coercion to work, each step toward the bomb must eventually be offset with a promise of nuclear forbearance. Otherwise, there is no reason for the United States to concede. This tension between making threats and assurances credible only becomes harder to resolve as potential proliferators approach the nuclear weapons threshold. The more nuclear capability they acquire, the more they need to offer greater nonproliferation commitments. The nuclear program itself often needs to be frozen, demobilized, or rolled back in some way.
In signing on to the 2015 Joint Comprehensive Plan of Action (JCPOA), Iran committed to never building nuclear weapons and took a series of steps that curtailed its latent capacity to do so. Notably, under the nuclear deal, it culled almost two-thirds of all operational centrifuges, gave up most of its LEU stockpile, converted the hardened Fordow facility to focus on medical isotope production, poured concrete into the Arak heavy-water reactor core, and accepted one of the most intrusive monitoring and verification regimes ever devised. Iran had to go to great lengths to illuminate the nuclear program and had to accept the security risks associated with letting potential adversaries closely monitor a wide range of activities.
This Iran case illuminates a key challenge with making such extensive nonproliferation commitments: leaders often cede control to elite stakeholders or activate domestic public support to build nuclear projects, which ends up entrapping them in “sticky” courses of action that are costly to overturn. Leaders in Tehran activated public support for the nuclear program on nationalist prestige grounds, as well as empowered a critical coalition of scientific, political, and military elites with the resources and autonomy necessary to master the front end of the nuclear fuel cycle. As a result, president Hassan Rouhani and the nuclear negotiation team ran into domestic opposition during this period as they probed various steps for rolling back nuclear latency in the lead up to the JCPOA.
As the basic contours of the final nuclear deal came into focus, some elites and military commanders mounted a vociferous opposition campaign, warning that Iran was giving up too much of the nuclear program in exchange for minimal concessions. The pushback from regime hard-liners may have been a deliberate ploy to improve Iran’s bargaining position, using domestic politics to tie the negotiators’ hands on the international stage. But regardless of the main reason, Supreme Leader Ayatollah Ali Khamenei had to play an active role in lowering these domestic costs for Rouhani and the negotiators; and he did so by advocating flexibility while drawing redlines around acceptable constraints. As nationalism and elite infighting intensified over the fate of Iran’s mature nuclear program, costly interventions from Khamenei appear to have been instrumental in enabling the Iranian negotiators to offer credible nonproliferation assurances.
There appears to be a sweet spot along the latency continuum where leaders should be in the best position to make both their threats and assurances credible. The boundaries of this spot align with the capacity to produce the fissile material at the heart of an atomic weapon. Once a nuclear program develops all the concrete capabilities needed to traverse down either the enrichment or reprocessing pathway, it becomes harder for the United States to inhibit proliferation with unilateral measures alone. Each step forward increases pressure on Washington to cut a diplomatic deal before it is too late. At this modest level of latency, however, the potential proliferator should still be able to make credible nonproliferation assurances. Domestic politics is less likely to distort the incentives leaders face when it comes to limiting the nuclear program.
Consider the initial success of North Korea in learning how to use its budding nuclear program to acquire concessions from the United States. When Pyongyang acquired plutonium production capabilities in the early 1990s, it used various mobilization tactics to gain leverage over Washington—from starting an NPT withdrawal countdown clock to preparing to reprocess plutonium from spent nuclear fuel rods at the Yongbyon complex. Yet North Korea was also in a prime position to offer promises of nuclear restraint because it could simply freeze the plutonium program prior to producing large quantities of weapons-usable fissile material. At this level of nuclear latency, Pyongyang seemed to effectively manage the tension between making threats and assurances credible, which set the foundation for the quid pro quos formalized in the 1994 U.S.-North Korean Agreed Framework. However, once North Korea’s nuclear program left this sweet spot by producing large quantities of plutonium during another bout of contentious diplomacy in the 2000s, it became increasingly costly and unattractive for the country’s regime to reverse course or even freeze activities.
In analyzing countries’ successes and failures, it appears that the leverage states gain from latency resembles a parabolic—or upside down “U”—curve when plotted across the nuclear capability continuum: there are few bargaining advantages at low and high levels of latency, but there is potential for significant benefits in the middle zone. This key finding undermines the notion that more power or capability is better for extracting concessions from superpowers. States need enough nuclear latency to underwrite threats, but not so much that it impedes their ability to make believable assurances.
How Should Washington Respond to Allies and Partners Who Leverage Latency?
At the moment, Iran is the only major U.S. adversary accumulating nuclear latency in lieu of the bomb. After the administration of president Donald Trump reneged on the JCPOA, Iran slowly resumed some limited nuclear activities in an apparent attempt to persuade Washington to come back into compliance with its obligations under the deal. But these efforts fell flat. Today, Tehran no longer seems interested in using uranium enrichment to gain additional bargaining power over Washington, preferring instead to experiment with the possible deterrent advantages from its nuclear threshold status. Meanwhile, several U.S. allies and partners face growing incentives and better opportunities to flex their nuclear options. Washington may find itself confronting a situation similar to the early Cold War, when key allies nurtured nuclear aspirations to shore up security commitments from anxious U.S. officials.
The signals coming out of Seoul and Riyadh last year indicated a shift in who is most likely to employ nuclear latency against Washington. Yet, even though they are the prime candidates for leveraging latency today, South Korea and Saudi Arabia lack industrial scale enrichment and reprocessing capabilities. Nuclear energy programs are more vulnerable and open to policy change at this stage. This should give U.S. officials a stronger hand to make any concessions conditional on Riyadh adhering to stricter nonproliferation obligations, or in Seoul’s case, simply continuing to uphold its long-standing nonproliferation bona fides.
Despite lacking fissile material production capabilities, however, Seoul seems to be relatively adept at using the prospect of proliferation as a diplomatic lever over Washington. The country boasts one of the world’s most advanced civil nuclear energy enterprises, along with conventional strike and space launch capabilities that could be converted into nuclear delivery systems. South Korea certainly has the technical capacity to build large enrichment or reprocessing facilities if it so desires. But restrictions in U.S.-Republic of Korea (ROK) nuclear cooperation agreements have prevented Seoul from moving beyond small-scale enrichment and reprocessing experiments—essentially keeping South Korea out of the sweet spot for leveraging latency against the United States.
Seoul therefore had just enough technical capacity to give its nuclear musings some weight last year, but not so much that it could extract substantial changes in the alliance architecture from Washington. Indeed, at the U.S.-ROK summit in April 2023, Yoon managed to secure several new promises from President Joe Biden to strengthen the U.S. force posture against North Korea. Most notably, Washington agreed to establish a bilateral Nuclear Consultative Group (NCG) to regularly discuss nuclear weapons matters. In exchange, Seoul recommitted to the NPT and its long-standing decision to depend on the U.S. extended nuclear deterrent. But this deal was viewed as a mere consolation prize in some quarters of Seoul, underscoring the perception that Yoon failed to wrest more meaningful concessions from the Biden administration.
By contrast, the source of Saudi leverage comes from factors beyond the four corners of its nascent nuclear program. Unlike South Korea, the country has no real nuclear latency to leverage. It is still working to start a new research reactor while penning ambitious plans to import nuclear power plants and even enrich indigenous sources of uranium. Saudi Arabia’s nuclear weapons flirtations have yet to yield any dividends in part because the notion of the kingdom going nuclear is simply not credible. To follow through with the threat, Riyadh would potentially have to torch supplier relations with Washington while running serious risks of conflict with Iran and perhaps even a shadow war with Israel. Of course, the Hamas terrorist attack in Israel on October 7, 2023, and the subsequent Israeli bombardment of Gaza froze a major U.S. effort to normalize Israeli-Saudi relations. The surprising rumor, though, according to multiple reports, is that prior to October 7, Riyadh may have persuaded the Biden administration to at least consider supporting some sort of enrichment program based on Saudi soil as part of a larger diplomatic parlay with Israel. This deal now seems to be on ice.
In this context, Riyadh’s bargaining power seems to come from pulling several geopolitical levers. Saudi Arabia often mentions the potential to move closer to Moscow or especially Beijing, its role as a major purchaser of American weapon systems, its influence over petroleum prices in a U.S. election year, and the United States’ desire to reshape relations in the Middle East. Although details on the rumored enrichment program are murky, it would have likely cut against the grain of long-standing U.S. efforts to keep countries out of the fissile material sweet spot. In an odd twist, U.S. officials seemed willing to foster an enrichment capability that Riyadh could then leverage in the future to compel additional concessions from Washington. Perhaps the Biden administration saw making a historic breakthrough in the Israeli-Saudi relationship or preventing Riyadh from pivoting toward Moscow or Beijing as worth the risk. But such a move would have perhaps emboldened other nations who are geopolitical lynchpins for Washington to follow in Riyadh’s footsteps.
Going forward, the United States should be prepared to deal with several long-term consequences of its approach to managing the South Korean and Saudi nuclear gambits. The most immediate concern is whether the deal cut at the U.S.-ROK summit last April will actually decrease demand for nuclear weapons in South Korea. As other scholars have warned, efforts to shore up the U.S. extended nuclear umbrella over South Korea could backfire if they end up stoking fears of entrapment in Seoul, thereby leading South Korean political elites to reconsider independent nuclear weapons.
If the United States eventually decides to support Saudi enrichment, it must be prepared to give Riyadh even more concessions to prevent advancements toward the bomb in the future. It must also be prepared to manage a wave of demands to pursue fissile material production capabilities—from critical allies such as South Korea and perhaps even anxious nuclear newcomers like Poland. Washington may find it difficult to keep its allies and partners from developing such capabilities after helping Saudi Arabia to become a latent nuclear power. Beyond the obvious proliferation risks, the spread of sensitive nuclear fuel cycle technology would leave the United States with far less bargaining power over allies and partners during an era of growing security competition.
The views in this article are the author’s own and do not reflect those of the U.S. Department of Defense or the U.S. government.