TWO

The New Start agreement, signed by the then US president Barack Obama and Russian president Dmitry Medvedev (Vladimir Putin was then prime minister) in 2010, was the last in the line of successive treaties that has reduced each power’s respective hoard of deployed warheads from 12,000 in the early 1990s to 1,550.

The deal monitors all three nuclear weapon delivery systems: intercontinental ballistic missiles (ICBMs), submarine-launched ballistic missiles (SLBMs), and bombers.

It also agreed rules around transparency, including the provision that each country would hold 18 on-site inspections of its nuclear weapons a year.

In 2023, Putin suspended Russia’s participation in the treaty, halting inspections and data exchanges. However, both sides have signalled they have kept within the numerical limits on the treaty. Presently, the US has 1,419 deployed strategic warheads while Russia has 1,549.

Last September, Putin said Russia was prepared to maintain the numerical limits of the treaty for one more year if the US “acts in a similar spirit”. But in January, the Kremlin said it had still not received a response from Trump.

With no talks in the works, the US president’s attitude as told to The New York Times last month was: “If it expires, it expires. We’ll do a better agreement.”

Nikolai Sokov, who worked on Cold War nuclear arms treaties from the Russian side, and who is now a senior fellow at the Vienna Centre for Disarmament and Non-Proliferation, said: “No one is even talking about negotiations, except for very general statements… The problem is we’re losing all kinds of predictability that we used to have.”

The treaty expires at a time when Putin has already been using nuclear threats to pressurise the West over its support for Ukraine.

The Russian leader has placed nuclear weapons on heightened alert and announced that Russian nuclear weapons will be deployed in Belarus.

He has also been investing heavily in new delivery systems, such as Russia’s Oreshnik intermediate-range ballistic missiles that can travel at 2.1 miles a second.

Without a nuclear disarmament treaty in place, the first thing that the US and Russia are likely to do is rapidly increase the number of warheads.

Both countries have much larger stockpiles beyond what they have loaded onto missiles. These include “non-deployed and retired warheads” – those which cannot be launched at the touch of a button – with the US storing 5,225 and Russia 5,580. Combined, they hold 87pc of the world’s nuclear weapons.

In the short term, simply by uploading more of its existing warheads onto its ICBMs, SLBMs, and bombers, each side could double its logistically deployed warheads to somewhere around 3,000 each within a year or two.

So, the big question now is to what extent each country ramps up its overall holdings and develops new weapons at a time when relations are frayed.

The view of Chatham House’s international security programme is that the direction we’re headed towards is a “new, unconstrained, nuclear arms race… Not only does that mean that we could be looking at a world with a lot more nuclear weapons like we had in the Cold War, but also this will be without verification and transparency measures and without dialogue. That also increases the risk of miscalculations and escalations.”

Nuclear arms experts in the West are unanimous in their warnings about a fresh 21st-century weapons race, which would put the Cold War in the shade. A commonly held view is that even during the height of the Cold War, NATO kept up its nuclear arms control co-operation. If there are no negotiated restraints on the nuclear capitals, then one should be afraid that we could be on the cusp of a nuclear arms race.

THREE

Thousands of miles away from Moscow and Washington, Xi Jinping displayed his pomp and ceremony last September as thousands of soldiers and weapons filed past him during China’s Victory Day Parade.

For seasoned nuclear watchers, the Chinese president’s statecraft included a startling sight.

Among the weaponry was a full nuclear triad of systems with submarine capabilities, plus five new intercontinental range systems – the first time China had displayed such an arsenal.

With the US having only five intercontinental range systems at home, some in Washington believe that was a clear signal to say that China can hold the US homeland at risk.

As Russia and the US duel it out, leaders in Beijing are quietly preparing for the impending arms race. Although China’s stockpile of nuclear warheads is still dwarfed by Russia and America, Xi has been ramping up his nuclear capabilities at a breathtaking pace.

In 2019, China had 290 nuclear warheads, according to the Federation of American Scientists. By 2025, it had 600. China now holds roughly twice as many warheads as France, which is the fourth largest nuclear power.

The Pentagon estimates that China will have more than 1,000 warheads by 2030. It has warned that China’s stockpile might hit 1,500 by 2035.

Xi is not only ramping up warheads but also China’s ability to deliver these weapons to their targets.

In the past six years, China has increased its number of ICBM launchers from 90 to 550, Pentagon assessments show. It has also increased its intermediate-range ballistic missiles (IRBMs) from 120 to 550.

For many observers, the turning point came in 2021, when scientists uncovered that the Chinese were building vast fields of nearly 300 silos to store ICBMs in western China.

This was revealing not just in the scale of China’s build-up, but its intent.

China officially has a “no first use” policy, claiming that it will never be the first one to strike. The ICBM silos suggest otherwise.

Silos sit in the ground and are unmovable, which means out of all of the delivery systems in a nuclear triad they are the most vulnerable to a first strike. In other words, they are not a particularly effective second-strike weapon. It would seem in line with first-use nuclear weapons.

FOUR

Another theory is that the silos are meant to serve as a nuclear shield.

If this is the case, it is a warning sign for Taiwan, which Xi has vowed to reunify with China.

Xi could be planning for the silos to act as a kind of sponge for a nuclear response if China made a move on Taiwan, soaking up strikes before Beijing can hit back. The idea is the adversary would launch a lot of their nuclear weapons at these silos, which would massively deplete the adversary’s forces.

Having an arsenal of weapons that can reach the US could also be designed to deter the US from coming to Taiwan’s defence. The US and Russia have what is known as a “prompt, first strike” relationship, which means they both keep similar numbers of warheads on very high alert, so that if one tries to launch, the other could launch on the warning. This is known as “first strike stability”.

The concern is that China is not just building up retaliatory forces, but that it wants to have that kind of mutual vulnerability with the United States.

Since he came to power in 2012, Xi has pursued a massive agenda of military modernisation.

In 2012, China’s military spending was a sixth of that of the US. By 2024, it was a third, at about $318bn (£233bn), according to the Stockholm International Peace Research Institute (Sipri). China’s battleship fleet surpassed America’s in 2014 and is expected to grow by a massive 48pc by 2030.

In January, Xi placed China’s top-ranking General under investigation in an extraordinary purge. The move says something either to do with serious corruption or an effort to consolidate his power, or both.

China’s nuclear rise has sudden and incredibly dangerous implications in an era when the world’s two largest nuclear powers have no caps on their stockpiles.

The rise of China, rather than Russia, will be the biggest potential driver of America’s need to increase its strategic arsenal. It’s what is known as the two nuclear peer problem, because the US must simultaneously deter Russia and China.

In the absolute worst-case scenario is where the US worries about China and Russia colluding during a time of crisis and would use this two-peer pressure to put America in a situation that would allow China to make a grab at Taiwan and would allow Russia to make landgrabs at NATO countries in Europe.

Yet, if America tried to build a nuclear deterrent large enough that it could theoretically win a nuclear war against both China and Russia separately, it would destroy any hope of first-strike capability. Everybody would be building towards this impossible outcome. You can’t have three nuclear powers that each have the same number of weapons as the other two. It’s mathematically impossible.

Xi and Putin are allied, but although they have declared a “no limits” partnership, meaning that no areas of cooperation are out of bounds, analysts say there is not enough trust between them to pursue a joint nuclear force. Both would be constantly increasing their stockpiles in an attempt to compete with America on an individual level, and America would be constantly increasing its stocks to out compete them both together.

We’ve never had a triangle in the history of the nuclear age. The triangle is inherently unstable. You can deter one, but you cannot deter two.

Previously, Trump said he would “believe very strongly in extreme military strength” and “wouldn’t trust our allies”. But since returning to office, the US president’s policy on nuclear weapons has been unclear. He has made few statements on nuclear issues and his National Defence Strategy made few mentions of nuclear arms. In a Truth Social post at the end of October, just before he met Xi in South Korea, Trump also took an inflammatory stance.

“Because of other countries testing programmes, I have instructed the department of war to start testing our nuclear weapons on an equal basis. That process will begin immediately,” he wrote.

Nuclear experts were confused. The department of defence is not actually responsible for nuclear testing.

That role belongs to the National Security Administration, which sits in the department of energy, which has responsibility for nuclear warheads.

Restarting nuclear weapons testing would also be a major national security mistake. China and Russia would probably follow suit. China, which has conducted fewer tests, would have far more to gain than the US in terms of how to build better weapons because it has less data to draw from past testing.

And it seems that Trump has not prioritised nuclear arms expertise in his administration.

Christopher Yeaw, an assistant secretary of state for the arms control Non-Proliferation Bureau, was only appointed by Trump a month ago.

Until then, the role had been vacant since Trump’s inauguration. Many long-standing experts were laid off during last year’s department of government efficiency (DOGE) cuts.

Trump’s wariness on nuclear weapons is apparent. White House officials point to the president’s stated desire to address the threat that nuclear weapons pose to the world and say Trump will decide the path forward on nuclear arms control on his own timeline.

That wariness comes to the fore when Trump speaks of China’s ascent: “I actually feel strongly that if we’re going to do it, I think China should be a member of the extension. China should be part of the agreement.” Trump made those comments last month. He has raised nuclear arms in his talks with Putin and Xi over the past year.

China insists, however, that they cannot participate in arms control agreements until they have parity with the US and Russia.

FIVE

Trump’s plans for his Golden Dome missile defence shield, which the president has promised will “deploy next-generation technologies across the land, sea, and space”, make the situation even more febrile.

China and Russia perceive the Golden Dome project as being very escalatory and destabilising. Such a view would bar any progress towards nuclear arms control.

The president pledged that the shield would take three years to build. In reality, work has barely started. But, undoubtedly, it is the thought that counts.

One of the biggest ironies of the last four decades is that when the United States announces a big missile defence plan, ultimately it fails. But when they announce it, the Russians take it seriously.

The prospect of stronger defences means higher-tech missiles in order for countries to maintain credible deterrents. If there is this sense that missile defence is gaining traction, then that too feeds a nuclear arms race.

Trump’s distrust of America’s allies in Europe and Asia also complicates the picture.

America protects its partners – such as members of NATO, as well as South Korea, Japan, and Australia – under what is known as its nuclear umbrella. This means that America has committed to defend these countries if they come under nuclear attack.

Under Trump, there are fears these guarantees are becoming less reliable. If Europe decides that it needs its own credible deterrent, its two nuclear powers, France and the UK, will have to scale up their arsenals.

That would mean the UK having to build at least four more submarines to have at least eight, and have something in the air.

Britain and France are small fry in the scheme of things, but that is actually its own source of anxiety for Russia.

Russian military thinking is that confronting small nuclear powers is inherently very dangerous, because the smaller nuclear powers will strike first just out of the fear that they would lose all of their nuclear weapons to the first strike of a bigger power.

SIX

There could also be a proliferation of new nuclear states.

South Korea is particularly likely to join the fray. In 2023, its president said that South Korea would consider building nuclear weapons itself if North Korea’s nuclear threat grows.

South Korea doesn’t trust American security guarantees as much as they used to. And generally, when the world is becoming one big mess, Pyongyang believes it has to look after itself and cannot rely on others.

If South Korea began weapons development, Japan could follow suit. Nuclear proliferation would drastically increase the risks for the world. There would be less trust and more opportunities for accidents; that is what is making this potentially more dangerous than the Cold War.

Trump may pride himself on making deals, but his mercurial negotiating style does not bode well for nuclear arms.

People might say it’s good to keep your adversaries guessing. But it can also lead them to draw false conclusions about what your intentions are.

One of the biggest fears that we should all have is a nuclear war that actually happened by mistake. Nuclear proliferation greatly increases that risk.