World enters nuclear uncharted waters as U.S.-Russia New START treaty expired

The world has entered uncharted waters after the last remaining arms control treaty between the United States and Russia expired on Wednesday, removing all legally binding limits on the two largest nuclear arsenals and raising fresh fears of strategic instability at a time of heightened global tension.

United Nations Secretary-General António Guterres on Wednesday described the lapse of the New START treaty as a “grave moment” for international peace and security, urging Washington and Moscow to urgently negotiate a new framework for nuclear arms control.

The New START treaty was signed in April 2010 in Prague by then U.S. president Barack Obama and Russian president Dmitry Medvedev, it entered into force in 2011, and was extended once, in 2021, for a final five-year period.

New START, which expired at midnight on Wednesday, capped the number of strategic nuclear warheads that the United States and Russia could deploy, as well as the deployment of land- and submarine-based missiles and heavy bombers designed to deliver them.

“For the first time in more than half a century, we face a world without any binding limits on the strategic nuclear arsenals of the Russian Federation and the United States of America – the two States that possess the overwhelming majority of the global stockpile of nuclear weapons,” Guterres stated.

He warned that the dismantling of decades of arms control achievements “could not come at a worse time”, noting that the risk of a nuclear weapon being used is now the highest it has been in decades.

At the same time, Guterres said the treaty’s expiration also created an opportunity “to reset and create an arms control regime fit for a rapidly evolving context”. He welcomed signals from leaders in both Russia and the United States acknowledging the need to prevent a return to unchecked nuclear proliferation.

“The world now looks to the Russian Federation and the United States to translate words into action,” he said, calling on both sides to return to the negotiating table without delay and agree on a successor framework that restores verifiable limits, reduces risks and strengthens collective security.

Moscow criticises the U.S. stance

Russia said on Wednesday it remained open to diplomacy on nuclear security but would “resolutely counter” any new threats following what it described as a mistaken and regrettable decision by the United States not to continue observing the treaty’s missile and warhead limits.

The Russian Foreign Ministry said Washington had failed to respond to President Vladimir Putin’s proposal to continue complying with New START limits for another 12 months.

“Essentially, our ideas are being deliberately ignored. This (U.S.) approach appears mistaken and regrettable,” the ministry said in a statement.

While criticising the U.S. position, Moscow said it would act “responsibly and prudently” despite the absence of any legally binding limits on strategic nuclear weapons. Russia said it would base its actions on a careful assessment of U.S. military policy and the broader strategic environment.

At the same time, the ministry said Russia remained prepared to take “decisive military-technical countermeasures” if it identified additional threats to national security. It added, however, that Moscow was also open to political and diplomatic avenues for comprehensive stabilisation of the strategic situation, provided appropriate conditions for equitable and mutually beneficial dialogue emerged.

There was no immediate response from the United States to the Russian statement.

President Donald Trump has previously said he wants China to be included in any future arms control arrangements and has questioned why the United States and Russia should continue building new nuclear weapons, given that they already possess enough to destroy the world many times over.

The White House said this week that Trump would decide the future course of U.S. nuclear arms control policy and would clarify his position “on his own timeline”.

Fears of a new arms race

Security experts have warned that the expiration of New START could pave the way for a renewed arms race, potentially involving China as a major player alongside the United States and Russia.

With the treaty no longer in force, both Washington and Moscow are now free to increase the number of deployed missiles and add hundreds of additional strategic warheads, although analysts note that such expansions would face logistical challenges and take time to implement.

In the absence of a treaty framework providing stability and predictability, analysts say each side may find it harder to interpret the other’s intentions. This could trigger a spiral of mutual suspicion, in which both countries feel compelled to expand their arsenals based on worst-case assumptions.

Matt Korda, associate director for the Nuclear Information Project at the Federation of American Scientists, said, quoted by Reuters, that without an agreement extending New START’s key provisions, neither Russia nor the United States would face formal constraints if they chose to significantly increase their arsenals.

“Without the treaty, each side will be free to upload hundreds of additional warheads onto their deployed missiles and heavy bombers, roughly doubling the sizes of their currently deployed arsenals in the most maximalist scenario,” he said.

Korda added, however, that the treaty’s expiration did not automatically mean a new arms race, pointing to the high financial costs associated with nuclear weapons programmes.

Last-minute appeal

As the deadline approached, Pope Leo issued a last-minute appeal urging both sides not to allow the treaty to lapse. Speaking at his weekly audience, the first U.S.-born pope called on Washington and Moscow to abandon the logic of fear and distrust.

“It is more urgent than ever to replace the logic of fear and distrust with a shared ethic, capable of guiding choices toward the common good,” he said.

Sources: Reuters, BGNES

Caption: Activists attend a flash mob on the occasion of the 5th anniversary of the UN treaty banning all nuclear weapons at Brandenburg Gate in Berlin, Germany, 22 January 2026. They demand the abolition of all nuclear weapons. Words read: Nuclear weapons are prohibited! EPA/HANNIBAL HANSCHKE