The last remaining nuclear arms control treaty between the United States and Russia expired on Thursday, raising fears of a renewed arms race between the world’s two largest nuclear powers at a time of heightened global instability.
The 2011 Strategic Arms Reduction Treaty, known as New START, capped deployed strategic nuclear warheads at 1,550 each for Washington and Moscow and provided for inspections and data exchanges. Its expiration leaves the two countries without any binding framework governing their strategic arsenals for the first time since the Cold War.
“The end of the accord definitely doesn’t make the world safer,” said Pavel Podvig, a senior researcher at the UN Institute for Disarmament Research in Geneva. “The real loss will be transparency, which increases political risks.”
The treaty’s demise comes amid sharply deteriorating relations between Russia and the West following Moscow’s invasion of Ukraine, uncertainty over the US’s long-term commitments to NATO, and China’s rapid expansion of its nuclear capabilities. Other countries are also reassessing their security needs as geopolitical competition intensifies.
Although New START was extended in 2021 for five years, Russian President Vladimir Putin suspended formal participation in 2023, halting inspections and information-sharing while pledging to continue observing the treaty’s limits. In September, Putin said Russia would adhere to the treaty’s terms for another year after expiry if the US did the same. US President Donald Trump did not formally respond.
Russia’s Foreign Ministry said on Wednesday that both sides now assume they are “no longer bound by any obligations” under the treaty and are free to chart their next steps, though Moscow remains open to diplomatic efforts to stabilise the strategic situation.
Experts warn that the absence of legal constraints could quickly lead to nuclear buildups. “Both countries may revert to worst-case planning and upload hundreds more warheads out of fear the other is doing so,” said Mackenzie Knight-Boyle of the Federation of American Scientists, noting that both sides retain significant capacity to rapidly expand their deployed arsenals.
The debate in Washington remains divided. Some Republican lawmakers have privately urged Trump not to accept Putin’s proposal for a temporary extension, arguing it would constrain the US more than Russia and fail to address China’s growing arsenal. Others, including former US arms control negotiator Rose Gottemoeller, argue that even a short extension would help preserve stability while longer-term strategies are developed.
China, which is not party to New START, has rejected calls to join trilateral arms control talks, saying its nuclear forces remain far smaller than those of the US and Russia. The Pentagon estimates China could have more than 1,000 nuclear warheads by 2030, up from a few hundred at the start of the decade.
Without new agreements, analysts warn that unconstrained competition between Washington and Moscow could prompt other nuclear-armed states — including the UK, France, North Korea, and Pakistan — to expand their arsenals as well.
Russia has recently highlighted new weapons systems, including hypersonic missiles and nuclear-powered delivery vehicles, while the US has signalled it could resume nuclear testing if others do so. Both countries last conducted nuclear explosive tests more than three decades ago.
Despite the uncertainty, some experts believe diplomacy remains possible. “A deal to settle the war in Ukraine could open the door to broader talks on strategic stability,” said Ankit Panda of the Carnegie Endowment for International Peace. “The Russians will be interested in engaging in arms control.”
For now, however, the expiration of New START marks the beginning of a nuclear era defined more by uncertainty than restraint.