During the cold war, several industrialised countries considered acquiring nuclear weapons. America worked hard to thwart proliferation, using threats, economic incentives and security guarantees. Debates about going nuclear are growing louder once more in countries with threatening neighbours, from South Korea and Japan—in North Korea's and China's backyard—to Poland and Saudi Arabia, on Russia's doorstep. Even in Japan, talk of acquiring a bomb is no longer beyond the pale.
Strategists describe the current era as a "third nuclear age", messier and more combustible than the cold war. America faces the unprecedented challenge of simultaneously confronting two nuclear near-peers—Russia and China—and American concerns about China's build-up, more than Russia's nuclear threats, are driving doubts over the last remaining US-Russia arms-control treaty. The arms-control architecture of the cold war has broken down. The New START treaty, the last remaining pact between America and Russia limiting nuclear arms, expired in February 2026 with no replacement. Under New START, both sides were allowed 1,550 warheads primed on long-range launch vehicles. Donald Trump ignored Russia's suggestion that both sides abide by New START's limits voluntarily for another year; Marco Rubio, America's secretary of state, said "It's impossible to do something that doesn't include China." Existing nuclear states are building up and modernising arsenals. America's nuclear umbrella, which offers assurances of protection to vulnerable allies, is fraying. Russia's threats to use nuclear weapons in Ukraine helped usher in this new era. The "nuclear taboo"—the shared moral revulsion that has helped control the use of nuclear weapons—seems to be weakening.
The survivors of the atomic bombings of Hiroshima and Nagasaki, known as hibakusha, have been telling their stories for decades, hoping to bring about disarmament. Nihon Hidankyo, an association of hibakusha, received the 2024 Nobel peace prize for "demonstrating through witness testimony that nuclear weapons must never be used again". Hibakusha were also central to the International Campaign to Abolish Nuclear Weapons, which won the 2017 Nobel peace prize for pushing the United Nations to adopt a treaty barring the development, acquisition, stockpiling or use of nuclear weapons. Not one of the world's nuclear states has signed up. Japan has also refused to sign, despite believing it has a special responsibility as the only country attacked with nuclear weapons: it depends on nuclear deterrence facing three nuclear-armed states—China, Russia and North Korea. Fewer than 100,000 officially recognised hibakusha are now alive, down from a peak of nearly 400,000. The average age of the remaining survivors is 86.
American nuclear guarantees have long been dogged by the question of credibility. In 1961 Charles de Gaulle, then president of France, asked President John F. Kennedy whether he would be ready to "trade New York for Paris"—that is, risk American cities to defend a European ally. American assurances and cajoling were nonetheless enough to dissuade countries such as Sweden and Taiwan from joining the nuclear club during the cold war. Today Donald Trump has repeatedly cast doubt on whether America would come to the aid of other NATO members, and American officials visiting Japan and South Korea have been noticeably reticent about the status of nuclear protection.
Vipin Narang, a scholar of deterrence, coined the term "catalytic nuclear posture" to describe a strategy designed to trigger help from a superpower patron. Small nuclear powers commonly adopt this approach. During the Yom Kippur war in 1973 Israel signalled to America that it might use nuclear weapons, triggering a hasty American airlift of conventional arms. Sweden's secret cold-war nuclear programme likewise aimed not to defeat the Soviets but to raise the costs of invasion and make American assistance more likely.
By the early 1960s Swedish scientists were perhaps two years from building a nuclear bomb after years of secret work. Officials discussed hiding a plutonium-production plant in a vast rock cavern. Military commanders drew up plans for an arsenal of 100 tactical nuclear weapons--bombs, missiles and torpedoes--for use against a Soviet invasion fleet. America set what appeared to be a trap, offering enriched uranium-235 for civilian power at low cost, then pressing Sweden on whether it was planning weapons. Social Democrat leaders ultimately decided that a small arsenal would not deter the Soviets but would make them target Sweden, strain defence budgets and harm the country's moral standing. The programme was over by the mid-1960s. Sweden went on to join NATO in 2024.
China's nuclear build-up provides political cover for North Korea's own nuclear expansion, fuelling pressure in Japan and especially South Korea to develop their own nuclear weapons. Any Indian response to China's nuclear expansion would increase the nuclear threat facing China and probably trigger Pakistani countermeasures. China has escalated verbal attacks on America's policy of extended nuclear deterrence—the nuclear umbrella that reassures allies and discourages them from building their own bombs—even though this arrangement has long served China's interests by keeping America's allies non-nuclear.
Elbridge Colby, Donald Trump's undersecretary for defence policy, has argued that South Korea should take "primary, essentially overwhelming, responsibility for its own self-defence against North Korea" because America cannot fight North Korea and then be ready to fight China. He has said America should refrain from imposing sanctions on a nuclear-armed South Korea. Scott Sagan of Stanford University warns that a nuclear South Korea on a hair-trigger, facing a volatile neighbour, would create special risks: both sides already have pre-emptive strategies, and all new nuclear powers follow "a learning curve" of distinguishing false alarms from real threats.
Including warheads kept in storage, America and Russia both have more than 5,000 nuclear weapons. America has about 1,770 total deployed warheads. The Heritage Foundation, a think-tank, has called for America to more than double this to 4,625 by 2050. Vipin Narang, an official from Joe Biden's administration, has suggested a more modest deployment of up to 500 additional weapons, mainly to aim at China's new silos; Franklin Miller, a former Pentagon nuclear planner, thinks about 300 would suffice.
America is modernising all three legs of its nuclear triad: new Sentinel land-based missiles, Columbia-class nuclear submarines and B-21 stealth bombers, as well as upgrading command-and-control systems. Some projects are woefully late or over budget. In the short term, America can "upload" extra warheads from reserves onto existing weapons. It needs just days to put more air-launched cruise missiles into bombers, but months to install more warheads on submarine missiles. Converting the Minuteman III land-based missiles from one warhead each back to three would take about two years. In 2023 the Federation of American Scientists calculated that America could deploy some 1,900 more warheads in these ways, compared with 1,000 for Russia. Expanding America's total stockpile would take decades; it can make only scores of new warheads a year, whereas Russia can produce hundreds.
The 40-year process of shrinking global nuclear stockpiles is going into reverse. China is already expanding its arsenal; if America builds up in response, Russia is certain to follow. India may feel compelled to counterbalance China, and Pakistan to offset India.
The Nuclear Non-Proliferation Treaty (NPT) is a legal ban on the creation of new nuclear-armed powers, signed by 191 states. Rafael Grossi, the head of the IAEA, has called it "one of the last points of stability that we have" in a dangerous world. Despite this, rogue states caught sprinting for a bomb face crippling sanctions and military strikes. In an April 2026 interview Grossi confirmed that discussions about acquiring nuclear weapons are being held across a wide range of countries. A European diplomat listed a dozen countries believed to be seriously researching nuclear options, from northern Europe to Indonesia, Turkey and the United Arab Emirates. The diplomat predicted Germany would one day want a nuclear bomb "and will get one, because they cannot rely on the US".
Iran boasted of having all the elements needed for a nuclear bomb, including uranium enriched almost to weapons-grade, then asked the world to believe it had no intention of building bombs. Rafael Grossi appealed in vain for full access for IAEA inspectors, noting that in the atomic realm "promises are not enough". Iran's policy of ambiguity ended with America and Israel losing patience. Grossi visited underground Iranian nuclear complexes reduced to rubble and exchanged with Iranian officials and scientists later killed by air strikes and assassinations. He drew a lesson from the deaths of Middle Eastern leaders who sought nuclear arms in Iran, Iraq and Libya: rulers with nuclear ambitions should return to the negotiating table. Critics draw the opposite conclusion: the one ruler who defied the world to build nuclear-tipped intercontinental ballistic missiles—Kim Jong Un—is the one who is alive.
Common sense is the collection of prejudices acquired by age eighteen.