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It has now been more than 15 years — though it might feel a lot longer — since then-President Barack Obama gave a landmark speech in Prague pledging that the United States would take “concrete steps towards a world without nuclear weapons” and shift away from the Cold War mindset that placed these weapons at the center of the country’s national security strategy.
Though the rhetoric was bold — and would help award him a Nobel Peace Prize later that year — Obama’s vision was relatively conservative. He laid out no concrete steps toward that goal and conceded it might not happen in his lifetime, at a moment when the president was just 48.
But it undoubtedly fit the zeitgeist of the time. Even some of the staunchest Cold War hawks were arguing then that nuclear weapons were obsolete in a world where superpower competition was at a low ebb and leaders were more concerned about terrorists getting their hands on a loose nuke than a state deliberately using one. The administration was in the process of negotiating New START, a treaty under which both the US and Russia agreed to sweeping reductions in their nuclear arsenals.
In retrospect, however, Obama’s speech looks less like the dawn of a new era than an epitaph for a brief period of hope that was rapidly coming to an end. In a speech last month, Admiral Tony Radakin, the chief of the United Kingdom’s armed forces, said the world has entered a “third nuclear age.” The first was the Cold War, and the second was the post-Soviet period, which was “governed by disarmament efforts and counter-proliferation.” The third era — the one we’re in now — is defined by “the almost total absence of the security architectures that went before,” as Radakin put it.
This is an era in which both the US and Russia are spending heavily on new nuclear capabilities and China is rapidly building up its own arsenal; in which Russia is flagrantly using the threat of nuclear weapons as a tool of coercion in its ongoing war in Ukraine; in which North Korea has dozens of nukes and Iran is potentially close to developing one; and in which a number of US allies — unsure about the reliability of America’s security guarantees — are wondering whether they need a nuclear deterrent of their own.
It’s also one in which decades-old arms control agreements meant to limit nuclear proliferation are lapsing, with little momentum toward reviving or replacing them. Once the last of those agreements expires, there will be a real risk that the world could find itself in a new nuclear arms race — except instead of two nuclear rivals, as in the Cold War, there will be three, which is a far more destabilizing dynamic.
This is the era in which Donald Trump will be handed the nuclear codes on January 20, and with them the ability to launch a war that could wipe out human civilization. Trump, of course, has some experience with the job, including both nuclear diplomacy and brinksmanship. He also has an approach to foreign policy so erratic that it has prompted calls for more limits to be put on the president’s unilateral control over nuclear weapons use.
The global landscape has also changed significantly since the last time Trump took office. Ankit Panda, a nuclear security expert at the Carnegie Endowment for International Peace, put it simply: “The big change this time is that things are a lot worse.”
A more dangerous nuclear world
We can start with Russia’s invasion of Ukraine. While a nuclear weapon has not been detonated in the war, Russia has undoubtedly used the threat of them as a means to deter Ukraine’s international backers from intervening directly in the conflict. This has ranged from President Vladimir Putin’s frequent reminders about his nuclear arsenal — the world’s largest — to more concrete recent steps like lowering Russia’s official threshold for nuclear use and the recent use of the new hypersonic, nuclear-capable “Oreshnik” missile on the city of Dnipro.
How effective this saber-rattling has actually been is an open question. The risk of nuclear war is certainly one big reason why the US and its allies never seriously considered sending troops into Ukraine or imposing a no-fly zone over the country in the early days of the conflict. Either move would have risked putting the world’s two biggest nuclear powers in a direct military confrontation, possibly killing each other’s soldiers. But Washington’s gradual ramp-up in weapons aid and recent decisions to allow Ukraine to carry out long-range strikes on Russian territory has shown that the US is a lot less intimidated by Putin’s threats than it used to be.
Biden officials emphasize that this doesn’t mean there was never any reason for concern. According to journalist Bob Woodward, US intelligence officials believed at one point in 2022 that there was a 50 percent chance of Russia using a tactical nuke in Ukraine if the Russians were in danger of losing the southern Ukrainian city of Kherson. Russia did lose the city eventually, with no such nuclear response.
But there was no guarantee that’s how events would play out. In a recent interview, Mara Karlin, a former assistant secretary of defense, said that during the war, the world has been closer to nuclear use than it has been in “many, many decades” and that the worst-case scenario was only prevented by a “very delicate and complex set of engagements with senior Americans and senior Russian officials over the last few years.”
Whether or not Putin’s nuclear signaling has been successful, nuclear analyst Heather Williams of the Center for Strategic and International Studies told Vox that other governments observing the situation are likely to conclude that “Russia, for the most part, has gotten away with nuclear bullying. They haven’t really been held accountable by the wider international community.”
Without detonating a single warhead, Russia has been able to make use of its nuclear arsenal in an active conflict as no nation has been able to do before. And other countries are taking notice.
China’s buildup and the three-body problem
Nine countries are known to have nuclear weapons, but it is the US and Russia that still account for almost 90 percent of the world’s nuclear arsenal, which is why arms control has historically been a two-player game. But that is changing.
A 2022 Pentagon report first sounded the alarm that the size of China’s nuclear arsenal had doubled over the past two years to 400 warheads and could potentially reach 1,500 warheads by 2035, while an updated Pentagon assessment at the end of 2024 put the current size of China’s arsenal at 600. Satellite photos from China’s northwestern desert show a major recent expansion of what experts believe are ballistic missile silos.
This is a significant strategic shift. China has had nuclear weapons since 1964 but has traditionally kept its arsenal small, even as the Soviet Union and the US embarked on the Cold War arms race and China grew and modernized its military. Although Beijing now has the world’s second-biggest military budget after the US, China only overtook France to become the world’s third-largest nuclear power in 2020.
“We were accustomed to thinking about China as the lesser threat because they always kept their nuclear numbers low,” Rose Gottemoeller, former US undersecretary of state for arms control, told Vox. “Suddenly we’re wondering: Are they, in fact, racing to build up to our numbers?”
Tong Zhao, an expert on Chinese nuclear weapons at the Carnegie Endowment, says China’s buildup is less about military tactics than about sending a political signal, particularly to the United States, that it is a country to be taken seriously. Chinese leaders “think China now faces a fundamentally more dangerous external environment and somehow a greater nuclear arsenal could give China very broad leverage,” Zhao told Vox.
Regardless of its intentions, China’s buildup makes the already fraught business of international arms control that much trickier. Trump, in his first term, argued it was foolish to bind America’s capabilities through bilateral agreements with the Russians while China’s arsenal grew unabated. It also raises the question of whether, as some argue, the US needs enough nuclear weapons to deter both Russia and China, which would entail a much larger buildup.
China is not yet a nuclear “peer” of the US or Russia and won’t be even if the Pentagon’s highest estimates are correct. Counting non-deployed stockpiles and retired weapons still awaiting dismantlement, the US and Russia each have more than 5,000 warheads in their stocks.
But the entry of a third, relatively smaller player can actually make nuclear diplomacy harder. US-Russia deals like New START worked in part because the countries were at relative parity, could mirror each other’s concessions, and had a lengthy history of negotiating such deals. Such complementary dealmaking isn’t possible with Beijing — China argues that if the US wants to talk about nuclear limits, it should first come down to China’s levels. During the first Trump administration, the US pushed for three-way arms control talks between the US, Russia, and China, but there was little interest from the Chinese side. Beijing views binding arms control agreements as “a trap to unilaterally constrain China’s capability development,” Zhao said.
In addition to the dangerous US-Russia-China “three-body problem,” the new administration will have to contend with the familiar challenges of North Korea and Iran, each of which appears to be intensifying. Trump and Kim Jong Un may have fallen in love during the former president’s first term, but contrary to Trump’s claims, the North Koreans never agreed to and have not denuclearized. North Korea is believed to have around 50 nuclear weapons, and while it has not detonated one since 2017, recent tests show its long-range missile capabilities are improving, including some theoretically capable of reaching the mainland United States. The North Koreans may also be receiving new technology and assistance from Russia in exchange for sending troops and munitions for the fight against Ukraine.
As for Iran, the size of its nuclear fuel stockpile has grown dramatically since Trump pulled the US out of the Obama-era nuclear deal in 2018, and US officials now say it could produce enough weapons-grade material to make a bomb in one to two weeks, though creating a deliverable weapon would take longer. There’s also some growing concern that Iran might be more likely to race toward building a nuclear weapon in light of the blows its proxies in Lebanon and Syria have recently taken.
All this means that at a time when these risks are growing, the diplomatic guardrails set up to manage nuclear competition are looking a lot shakier.
The nuclear guardrails are not what they used to be
A number of significant nuclear arms control agreements met their demise during Trump’s first term. Most famously, Trump pulled the US out of the 2015 Iran nuclear deal, under which Tehran agreed to limits on its nuclear program in exchange for sanctions relief. Subject to less public debate, but also significant, were the Intermediate-Range Nuclear Forces Treaty — a Reagan-era deal that places limits on US and Russian missile forces — and the Open Skies Treaty, which allowed NATO and post-Soviet countries to conduct reconnaissance flights over each others’ territories to verify compliance with arms control. Trump pulled the US out of both, citing alleged Russian violations.
The last remaining US-Russia arms control agreement, New START, is still in effect, but barely — Russia suspended its participation in 2023 and the US partially followed suit soon after. Both countries say they are still complying with the treaty’s central limit on the number of nuclear warheads in their arsenals, but that could change when the treaty finally expires in February 2026. The Russians have shown little indication they are interested in negotiating an extension of the deal, even if the incoming Trump administration wanted to.
Other landmark arms control deals are still in effect but looking shaky. The future of the 1967 Outer Space Treaty, which prohibits placing weapons of mass destruction in space, was called into question this year by US intelligence reports indicating that Russia is developing an orbital nuclear anti-satellite weapon. In April, Russia vetoed a US-backed UN resolution that would have reaffirmed and expanded the treaty’s restrictions.
In 2023, Russia also withdrew from the 1996 Comprehensive Test Ban Treaty (CTBT), ratified by nearly 180 countries, which bans the live testing of nuclear weapons. US officials have also suggested China may have conducted some very low-yield nuclear tests.
Though President Bill Clinton signed the CTBT in 1996, Congress never ratified it. While the US hasn’t actually carried out a nuclear test since 1992, the Heritage Foundation’s Project 2025, a set of proposed policies for the new Trump administration, argues that the US should reject the CTBT and “indicate a willingness to conduct nuclear tests in response to adversary nuclear developments if necessary.” This is less out of technical necessity — modern nuclear weapons states have a variety of techniques they can use to verify the performance of nuclear weapons without actually detonating them — than a desire to demonstrate the credibility of the US nuclear deterrent.
The Biden administration had its last breakthrough with Russia in 2021 when the two countries agreed to extend New START until 2026, but Russia has rejected new arms control talks since the full-scale war in Ukraine began in 2022. Both the Trump and Biden administrations have made efforts to reach out to China for nuclear talks, but to little avail.
“People need to get it. Arms control is dead,” the Heritage Foundation nuclear policy research fellow Robert Peters told Vox.
The most pressing question now may be what happens in 2026 after New START, which limits the US and Russia to 1,550 deployed warheads and 700 deployed delivery vehicles each, finally expires. It’s an increasingly mainstream view in Washington that the US may need to build up.
The US is already in the midst of a 30-year, $1.5 trillion “modernization” effort that entails upgrades and replacements for all three legs of the country’s nuclear “triad”: ground-launched ballistic missiles, nuclear submarines, and strategic bombers, although without actually deploying more weapons beyond the New START limits. Though Secretary of Defense Lloyd Austin may have remarked early in the Biden administration that nuclear deterrence “isn’t just a numbers game,” it’s an increasingly mainstream view in Washington, expressed by both members of Congress and officials from the outgoing administration, that the new global threat landscape may require not just more modern nuclear weapons, but more weapons, period.
As Vipin Narang, former acting assistant secretary of defense for space policy, put it at a recent event, the modernization effort was “sized for a completely different security environment [and] may need to be reassessed in the multiple nuclear challenger world.” In other words, a world where both Russia and China have large nuclear arsenals and adversaries like North Korea and potentially Iran have smaller ones.
Trump talked about expanding the US arsenal in his first term, and the idea is likely to be back on the agenda in a second term. The new administration is “going to look at the same classified data that I think, is fair to say, scared the dickens out of the Biden administration team, and they’re going to read the documents that came out over the last 18 months, and they’re going to say, ‘Yeah, we do have to go up’” in numbers, said the Heritage Foundation’s Peters, himself a former Pentagon official.
“No, we don’t need as many nuclear weapons as Russia and China combined, but we do need more than what we’ve got today,” he added.
Not everyone agrees. Rose Gottemoeller, former undersecretary of state for arms control, said the ongoing modernization effort was demanding enough without adding new weapons. “If there are new demands placed on modernization, the whole modernization process could just collapse because it will be too expensive and too complicated,” she told Vox. “The defense industry complex and the nuclear weapons complex simply cannot take on additional requirements.”
But if current trends continue, including the Chinese buildup and a more aggressive Russian nuclear posture, the political momentum for a new arms race will grow, and the new administration seems far less likely to try to resist it.
A growing nuclear club?
Almost as remarkable as the fact that no country has used a nuclear weapon in war since 1945 is the fact that so few countries have acquired their own nuclear arsenals over the past eight decades. The 1968 Non-Proliferation Treaty, with over 190 ratifiers, recognizes five nuclear weapons states: the US, Russia, China, France, and the UK. Four other countries have since joined the club: India, Pakistan, North Korea, and Israel, the last of which is widely known to possess nuclear weapons but does not publicly discuss them.
Over the years, a number of countries have had nascent nuclear programs, including US adversaries like Iraq and Syria as well as allies like South Korea and Taiwan. In the case of the allies, the US used diplomatic pressure to dissuade them from actually building a bomb.
More than 30 countries, including members of the NATO alliance and US allies in the Pacific are covered by US defense guarantees, meaning they effectively get the benefits of US nuclear deterrence without the costs and dangers of developing their own nuclear weapons — though some do host American nukes on their soil.
But how much are those guarantees really worth in an increasingly dangerous world? Many Ukrainians believe it was a mistake for the country, 30 years ago last month, to give up the Soviet weapons that had been left on its territory in exchange for assurances from the US, Russia, and others that its sovereignty would be respected. (Ukraine never actually had operational control of these weapons, which could only be fired on orders from Moscow, but it’s a powerful narrative nonetheless.)
Ukrainian President Volodymyr Zelenskyy recently said that his country’s future security can only be guaranteed by either an effective security alliance — NATO, in other words — or a nuclear weapon. There’s now an active political debate in countries including Germany and Poland about whether Europe needs a more formidable and perhaps less American-controlled nuclear deterrent — particularly as Trump’s return raises questions about future US commitment to the alliance.
In South Korea, public support for developing a nuclear weapon is high, in light of perceived threats from both North Korea and China as well as doubts prompted by Trump’s return and his often dismissive attitude toward US defense commitments. In 2023, the US took steps to reassure South Korea with a landmark agreement to increase nuclear cooperation and consultation. Some of this consultation was temporarily suspended in light of South Korea’s recent political upheaval.
Even in Japan — the only country to have been the victim of a nuclear attack — Prime Minister Shigeru Ishiba recently called for a rethink of the country’s longstanding anti-nuclear principles and a debate on sharing or hosting nuclear weapons. If Japan ever decided to go nuclear on its own, it is thought to have the means to build one in just a few months — a capability some have called the “bomb in the basement.” Chinese military action against Taiwan might be just the sort of shock that prompts a nuclear rethink throughout Asia.
Saudi Arabia’s leaders have also said they will seek a nuclear weapon of their own if Iran builds one.
Panda, from the Carnegie Endowment, says past US efforts to dissuade allies from building nuclear weapons of their own were “not motivated by any highfalutin ideas about the rules-based international order. It’s because it’s in our own self-interest to have a world where there are fewer decision-making centers with nuclear weapons.”
The era when the number of those centers is relatively few may be limited.
A glimmer of hope
While the past few years have been a grim time for nuclear diplomacy, several experts who spoke with Vox noted that the Biden team has had some luck in raising nuclear issues in leader-to-leader contacts. This included an agreement during a recent conversation between Biden and China’s President Xi Jinping that humans rather than artificial intelligence should maintain control over decisions on nuclear weapons use.
That kind of informal agreement may be the best we can hope for at the moment, and it may be an approach that Trump — who is not one for formal security agreements and famously pursued one-on-one nuclear diplomacy of a very unusual sort with Kim Jong Un — might be able to take up. If a deal is eventually reached to end the fighting in Ukraine, a very big if at the moment, it’s also at least conceivable that a resumption of US-Russia arms control talks could be part of the settlement.
But for now, we appear to be headed toward a world where the number of nuclear weapons is increasing, as is their relevance to global affairs and the risk that one will actually be used — to catastrophic or even civilization-destroying effect.
As Sharon Squassoni, a professor and authority on nuclear risk at George Washington University, put it, “probably the most concerning part of this whole landscape is that we seem to have lost our concern about the risks that nuclear weapons pose.”
The third nuclear age is one in which we may have to relearn some forgotten lessons from the first.
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