The US and Russia let ‘START’ nuclear arms treaty expire. Experts say it’s a dangerous move
The expiration of the last remaining bilateral treaty between the U.S. and Russia to limit the number of nuclear weapons portends a more dangerous global security environment, Northeastern University experts say.
The expiration of the last remaining bilateral treaty between the United States and Russia to limit the number of nuclear weapons portends a more dangerous and uncertain global security environment at a moment of growing nuclear competition, according to Northeastern University experts.
The Strategic Arms Reduction Treaty, or START, was conceived in the aftermath of the Cold War as a way to rein in nuclear arsenals after years of weapons expansion. The treaty, first signed in 1991 (START 1) and later renewed in 2010 and 2021 (New START), worked to put a cap and significantly reduce U.S. and Russian nuclear arsenals, bringing numbers down to 1,550 per country, according to limits delineated in the agreement.
The pact helped to provide a sense of stability between the two powers for decades, said Northeastern University national security expert Stephen Flynn.
“The end of that treaty brings us back to those scary times and risks an arms race,” Flynn said. “Whereas the Cold War took place in a bipolar world, today we have China as a formidable nuclear force, and other countries looking to join the nuclear club.”
Indeed, the fact that there are more countries with nuclear weapons complicates efforts to negotiate a successor agreement, particularly as China’s growing arsenal and the ambitions of other countries introduce new strategic calculations, Flynn said. According to a 2025 report in the Bulletin of the Atomic Scientists, an independent scientific organization that tracks global nuclear arsenals and security risks, China possesses approximately 600 nuclear warheads, with more in production.
Whereas only five nations had nuclear weapons in 1991 — the U.S., China, France, the United Kingdom and the Russian Federation — there are at least nine countries today with nuclear capabilities and an active arsenal, according to the latest estimate from the Arms Control Association, a Washington D.C.-based nonprofit organization that monitors global nuclear arsenals and arms control developments.
Countries, such as India and Iran, have developed their own nuclear programs, or have aspired to produce nukes. India has roughly 180 nuclear warheads, according to an estimate from the Federation of American Scientists, a Washington, D.C.-based nonprofit that tracks the development of nuclear programs. Iran’s nuclear program has advanced enough to potentially produce weapons, though it currently fields none.
Unlike earlier arms control negotiations that focused on managing a single rivalry between Washington and Moscow, he said today’s landscape involves multiple actors with differing force sizes, doctrines and transparency standards, making it far more difficult to agree on limits, verification measures and enforcement mechanisms.
“Every time you add an additional party, you add orders of magnitude more complexity to the process,” Flynn said.
In a recent Truth Social post, President Donald Trump said that rather than extend START, which he described as a “badly negotiated deal,” nuclear experts should “work on a new, improved, and modernized Treaty that can last long into the future,” he said.
The president touted what he described as his administration’s success at completely rebuilding “the military during his first term, including “new and many refurbished nuclear weapons.” He also praised his administration’s work creating the U.S. Space Force, which became the sixth branch of the U.S. military focused on space operations.
Exactly what happens now, in terms of nuclear cooperation, remains uncertain.
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The White House reiterated Trump’s comments, referring back to his Truth Social post. Russian foreign minister Sergei Lavrov told the state-owned NTV news channel that Moscow would continue to act responsibly following the termination of the treaty, but would closely monitor the actions of the U.S., the Russian state news agency, TASS, reported.
But Flynn said there is typically “years of work” in advance of the treaty’s renewal deadline to ensure the terms are robust.
New START talks emerged from earlier Cold War-era arms control efforts between the U.S. and the Soviet Union, such as a series of agreements reached through the Strategic Arms Limitation Talks, or SALT, in the 1970s. Those talks slowed the growth of both arsenals and introduced verification measures that reduced the risk of miscalculation. Subsequent START treaties expanded on that framework by shifting from limits on expansion to deep, negotiated reductions in nuclear forces.
Russia’s invasion of Ukraine in 2022 strained relations between the two superpowers and disrupted decades of nuclear arms control. In 2023, Moscow suspended its participation in New START by halting inspections and data exchanges, a move that complicates any extension or successor agreement, Flynn said.
“It is regrettable that the START Treaty has expired due to the inaction of the two most heavily armed nuclear powers,” said Denise Garcia, professor of political science and international affairs, who added that the event “marks a concerning low point for global diplomacy on nuclear weapons limits.”
News of the treaty’s expiration is especially troubling in light of Trump’s comments about restarting nuclear testing, Garcia noted.
Flynn said the expiration of the treaty threatens not only formal limits on nuclear weapons, but also the norms that have governed nuclear restraint for decades. Without an arms control framework in place, he said, the shared understanding that nuclear weapons are catastrophic tools meant never to be used in war begins to erode, increasing the risk that states view them once again as usable instruments of conflict instead of weapons of last resort.
But, Garcia noted, it is not all grim, adding that there are other important elements of the international legal architecture to contain nuclear weapons, such as the 1968 Nuclear Non-Proliferation Treaty, or the NPT.
“This is the cornerstone treaty to limit global proliferation and mandates countries to come to a nuclear zero,” Garcia said.
