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In the face of Russian and Chinese aggression, allies and at-risk nations are reconsidering the power of deterrence.

“I am haunted by the feeling that by 1970,” President John Kennedy sighed in the springtime of , “there may be 10 nuclear powers instead of four, and by 1975, 15 or 20.” Such a world, he warned, would represent “the greatest possible danger.”

A range of initiatives –&�Բ�����;the Nuclear Nonproliferation Treaty, the Nuclear Test Ban Treaty, the Cooperative Threat Reduction Program, inducements and supervised civilian nuclear development, sanctions and international monitoring, and   in some cases –&�Բ�����;staved off Kennedy’s nightmare scenario. As a result, there were just five by 1970, seven in 1980, 10 in 1992, seven in 1995, nine in 2006. 

However, the nightmare is returning, as three factors accelerate the erosion of the already-shaky nuclear-nonproliferation regime. First, nuclear-weapons knowhow, materials and technology are no longer tightly controlled by a small handful of nation-states in the  . Second, those outside the club have seen what can happen to nation-states that don’t possess a nuclear deterrent. (Ukraine is the most recent example.) Third, there are   surrounding America’s  .

These factors are conspiring to spawn a much larger nuclear club –&�Բ�����;and a much more dangerous world.

Next to join the club In 1994, Ukraine surrendered its entire nuclear arsenal in exchange for Russia’s commitment to “refrain from the threat or use of force” and respect Ukraine’s “sovereignty” and “existing borders.” The free world’s failure to back up those words after Putin’s 2014 attack on Ukraine not only set the stage for 2022; it crippled the cause of nuclear nonproliferation. Russia’s war on Ukraine serves as an object lesson of the deterrent power of nuclear weapons –&�Բ�����;and the danger of not having them. Allies like South Korea and Poland, war-scarred nations like Ukraine, at-risk nations like Taiwan, and adversaries like Iran are pondering that lesson.

Ukraine –&�Բ�����;President Volodymyr Zelensky of Ukraine recently declared, “Either Ukraine will have nuclear weapons and that will be our protection, or we should have some sort of alliance.” That’s not a bluff: Ukraine has the infrastructure –&�Բ�����;intellectual, economic, industrial, technological, scientific –&�Բ�����;to build a nuclear weapon. And arms-control experts that Ukraine has long possessed weapons-grade plutonium at existing nuclear-power facilities. 

Poland –&�Բ�����;Prime Minister Donald Tusk of Poland stunned the world by in March that his country “must pursue the most advanced capabilities, including nuclear and modern unconventional weapons.” As with Ukraine, Poland has the necessary infrastructure to build or buy a nuclear deterrent. And as with Ukraine –&�Բ�����;and virtually all of Russia’s neighbors –&�Բ�����;Poland has sound justifications for going nuclear: Russia has simulated nuclear strikes against Poland, that western Poland was “a gift from Stalin,” destabilized the region by recklessly moving nuclear weapons into neighboring and, of course, attempted to conquer Ukraine.

Germany –&�Բ�����;Asked if Germany should build its own nuclear deterrent, incoming Chancellor Friedrich Merz would only say, “There is no need for this today.” As The Wall Street Journal reports, Merz’s response raised eyebrows and “broke with a longstanding taboo.” A key post-Cold War bars Germany from “the manufacture … possession of and control over nuclear, biological and chemical weapons.”

For now, Merz is making to France and Britain (the only nuclear-armed NATO members other than the United States) to extend their nuclear deterrent to cover Germany. One option Germany is is for France to deploy its nuclear-armed aircraft to Germany. Known as “nuclear sharing,” this sort of arrangement has enabled the United States to extend deterrence to Germany and other allies for decades. Citing what he “the changed global security situation,” Merz Germany is entering into discussions with Britain and France “about whether nuclear sharing, or at least nuclear security from the U.K. and France, could also apply to us.” 

President Emmanuel Macron of France has indeed proposed extending the across Europe, though , as of this writing, has not publicly echoed Macron’s proposal. France has a total inventory of (configured for delivery by submarines and bomber aircraft). Britain has a total inventory of (all of which are configured for delivery by submarines). The limited numbers and limited modes of delivery suggest it would be a stretch for France and/or Britain to provide viable a continentwide nuclear deterrent –&�Բ�����;at least as currently postured.  

The Nordic and Baltic countries –&�Բ�����;Similar to Germany, the Swedish government has France’s “openness” to extending its nuclear umbrella across Europe and interest in nuclear-sharing arrangements. Even more eyebrow-raising: One of Sweden’s leading newspapers recently began what it a “discussion about nuclear weapons,” openly asking whether “we need to acquire a nuclear deterrent of our own, perhaps in cooperation with our Nordic neighbors.” Interestingly, Sweden maintained a secret nuclear-weapons development through the 1960s.

Danish Prime Minister Mette Frederiksen Macron’s nuclear proposal, and Lithuanian Prime Minister Gitanas Nauseda has said the French nuclear arsenal could provide “serious deterrence toward Russia.”

South Korea –&�Բ�����;“We could acquire our own nuclear weapons,” then-South Korean President Yoon Suk-Yeol said in 2023, mentioning the possibility of “deploying tactical nuclear weapons.” He’s not alone: In the runup to the June special election to replace Yoon, there are indications that both major parties are open to acquiring nuclear capabilities –&�Բ�����;not surprising given that of South Koreans support development of a homegrown nuclear deterrent. South Korea’s current foreign minister, Cho Tae-yul, bluntly in March that nuclear weapons remain Seoul’s "plan B" given the "unpredictable" security environment. None of this is mere public posturing: South Korea has a highly developed civilian nuclear program, vast financial and industrial resources, and a deep reservoir of scientific and intellectual capabilities.

Japan –&�Բ�����;There’s little public support in Japan for an indigenous nuclear deterrent. However, in the wake of Putin’s invasion of Ukraine –&�Բ�����;and –&�Բ�����;Japanese at the highest levels have support for nuclear-sharing arrangements with the United States. In addition, it’s worth noting that Japan has for decades maintained what arms-control officials euphemistically a “bomb in the basement” –&�Բ�����;the technological, industrial and material capabilities to go nuclear in case of emergency with the . 

Taiwan –&�Բ�����;Respected deterrence and strategists have raised the prospect of Taiwan acquiring or developing a nuclear arsenal to deter its behemoth neighbor. As with most of the nations discussed here, Taiwan has the requisite scientific, technological, financial and industrial means to go nuclear. Taiwan quietly maintained a nuclear-weapons development program until the early 1980s –&�Բ�����;and throughout the 1990s, Taipei sent that it could restart the program or even maintain a “bomb in the basement” capability. The United States  nuclear weapons on Taiwan during the Cold War. Thoughtful observers have a return to that posture. However, that would require a wholesale reversal of Washington’s long-held policy of strategic ambiguity.

Iran –&�Բ�����; and clandestinely developing nuclear weapons for decades, Iran could crash the nuclear club at any time. Indeed, in 2023, then-Undersecretary of Defense Colin Kahl that Iran could produce enough fissile material for a single nuclear weapon in “about 12 days.” An Iranian nuclear test would trigger a cascade of consequences, including nuclear blackmail by Tehran, military action by Israel and/or the United States, and a regional nuclear-arms race. Asked what would happen if Iran were to test a nuclear weapon, Saudi Crown Prince Mohammed bin Salman bluntly , “We will have to get one.” , Turkey and other Sunni states would likely follow suit.

Back on the brink On top of all that, Russia has violated the to the point of killing it. Russia has revised its military to lower the threshold for using nuclear weapons, recklessly and constantly engaged in throughout its war on Ukraine, and used Ukraine to field-test non-nuclear variants of a new medium-range nuclear-capable . Equally troubling, China has nearly tripled its nuclear arsenal since 2020, will mushroom its nuclear stockpile by 2030 and recently completed construction of a 300-silo ICBM field.

Add it all up, and the era of nuclear nonproliferation (and the relative stability it ensured) is giving way to a dangerous new era marked by nuclear breakouts and nuclear buildups. If history is any guide, those nuclear breakouts and buildups will lead to nuclear brinkmanship. 

The world is careening back toward the brink.