Nuclear arms race on the horizon? US, Russia's New START expires today — key things to know

The last remaining nuclear arms control treaty between the United States and Russia expires today, removing caps on the world’s two largest nuclear arsenals for the first time in decades and heightening fears of a new, unconstrained arms race.

The Strategic Arms Reduction Treaty — known as New START — was signed in 2010 and has been regarded as a cornerstone of strategic stability, limiting the number of deployed strategic nuclear warheads and providing transparency measures designed to prevent miscalculation between Washington DC and Moscow.

Those inspections were paused in 2020 due to the COVID-19 pandemic and never resumed. In February 2023, President Vladimir Putin suspended Russia’s participation in the treaty amid escalating tensions over the war in Ukraine, though Moscow insisted it would continue to observe the treaty’s central limits.

With the treaty now expiring, the formal architecture that constrained strategic nuclear deployments and provided verification is set to disappear entirely.

On Wednesday, the Russian foreign ministry said in a statement that “in the current circumstances, we assume that the parties to the New START are no longer bound by any obligations or symmetrical declarations in the context of the Treaty, including its core provisions, and are in principle free to choose their next steps.

“In doing so the Russian Federation intends to act responsibly and in a balanced manner,” the statement said, adding that Moscow “remains ready to take decisive military-technical measures to counter potential additional threats to the national security”.

Kremlin spokesman Dmitry Peskov said Tuesday it would be a “more dangerous” world without limits on US and Russian nuclear stockpiles.

Putin has previously argued the treaty’s expiration could accelerate proliferation, warning the collapse of constraints could encourage other states to seek nuclear weapons as a deterrent.

Last month, Trump told the New York Times: “If it expires, it expires… We'll just do a better agreement”.

A White House official said Monday that Trump has repeatedly indicated he would like to maintain limits on nuclear weapons, but wants China included in any future agreement. Trump will make a decision on nuclear arms control “on his own timeline”, the official said.

Beijing has resisted restrictions on its smaller — but rapidly expanding — nuclear arsenal. Moscow, meanwhile, has argued that any successor arrangement should also involve France and the United Kingdom, Europe’s nuclear powers.

On Wednesday, Pope Leo urged the US and Russia to renew the treaty, saying the current world situation required “calls for doing everything possible to avert a new arms race”.

They include:

In a speech last year he described the collapse of these key arms control treaties as “one of the most dangerous aspects of our current global security”, along with “the increasing prominence of nuclear weapons”.

Daryl Kimball, executive director of the Arms Control Association in Washington, said: “We're at the point now where the two sides could, with the expiration of this treaty, for the first time in about 35 years, increase the number of nuclear weapons that are deployed on each side.

“And this would open up the possibility of an unconstrained, dangerous three-way arms race, not just between the US and Russia, but also involving China, which is also increasing its smaller but still deadly nuclear arsenal.”

Kingston Reif of the RAND Corporation, a former US deputy assistant secretary of defense, warned during an online discussion that “in the absence of the predictability of the treaty, each side could be incentivised to plan for the worst or to increase their deployed arsenals to show toughness and resolve, or to search for negotiating leverage”.

Medvedev has also issued more explicit warnings, saying Russia would respond firmly if it faced new threats.

“Without agreements limiting nuclear arsenals, Russia "will promptly and firmly fend off any new threats to our security," said Medvedev, who had signed the New START treaty and is now deputy head of Putin's Security Council.

"If we are not heard, we act proportionately seeking to restore parity," he said in recent remarks.”

Darya Dolzikova, a senior Research Fellow with the UK-based RUSI’s Proliferation and Nuclear Policy Programme, said the expiration of New START was “concerning, because there are drivers on both sides to expand their strategic capabilities”.

She said that for Russia “there appears to be some concerns about their ability to penetrate US air defences” — concerns sharpened by Trump’s plans to build a “Golden Dome” missile shield to protect North America from long-range weapons.

Russia has developed systems designed to bypass missile defence, including Poseidon — an intercontinental, nuclear-armed and nuclear-powered undersea autonomous torpedo — and Burevestnik, a nuclear-armed and nuclear-powered cruise missile.

The US, Russia and China are also developing long-range hypersonic missiles capable of manoeuvring at speeds above 4,000 mph (6,437 kmh), making them harder to intercept.

Dolzikova said these expanding capabilities would “only make it harder” to negotiate a new arms control treaty.

The original START treaty signed in 1991 by the US and the Soviet Union barred each side from deploying more than 6,000 nuclear warheads. Earlier, SALT I in 1972 represented the first attempt to limit the superpowers’ arsenals.

Other key pillars have since fallen away. The US withdrew from the 1972 Anti-Ballistic Missile Treaty in 2001. The Intermediate-range Nuclear Forces Treaty — signed in 1987 — collapsed in 2019.

Those developments have left New START as the last remaining treaty limiting the two largest nuclear arsenals — until today.

The issue was reportedly raised when Putin met Trump in Alaska last year, but no breakthrough followed. Putin has said he was prepared to continue observing New START limits for another year if Washington did the same, though Trump has been noncommittal.

Rose Gottemoeller, the chief US negotiator for the pact and a former NATO deputy secretary-general, argued the United States should have accepted a temporary extension.

“A one-year extension of New START limits would not prejudice any of the vital steps that the United States is taking to respond to the Chinese nuclear buildup,” she told an online discussion last month.

(With agency inputs)