The New START treaty between the United States and Russia, which was signed in April 2010, limited the number of strategic nuclear warheads each country could have ready for launch to 1,550. It’s the latest in a series of agreements that reduced the US arsenal from a peak of more than 30,000 warheads in the 1980s. The treaty expires on February 5, and neither country has moved to replace it with a new agreement. We asked UCS Policy and Research Analyst Jennifer Knox about the implications.
AAS: How well did New START serve its purpose, and in its absence, what are both countries free to do?
JENNIFER KNOX: In the early years of the Cold War, the United States and the Soviet Union spent endlessly to outdo one another and build the largest and most sophisticated nuclear arsenal. That’s the nature of an arms race: Each step to secure an advantage over an adversary drives a response, nullifying the supposed advantage while introducing new threats that prompt further military investments. Escalating competition resulted in bloated arsenals of tens of thousands of nuclear weapons each—strategically pointless, shamefully wasteful, dangerously irresponsible.
We won’t create a safer world for ourselves or anyone else by endlessly building more weapons. The only way out of this destructive cycle is through cooperation. In 1972, the United States and the Soviet Union signed the first treaty to limit the numbers and types of nuclear weapons the two countries could put into launch position. Ever since, they have negotiated successive agreements to honor mutual restraints on their nuclear capabilities. Over time, strategic arms control allowed both countries to make massive reductions in their nuclear stockpiles. New START is the eighth such treaty and the last to remain in force.
Unfortunately, no legal agreement has been prepared to take New START’s place. Negotiating an arms control treaty takes months, if not years, of dedicated work. In this case, the negotiating process has stalled entirely, and the United States and Russia remain far apart on questions about what a future arms control treaty should (and could) address. When New START expires in February, the United States and Russia will face an extended period without any formal restrictions on their strategic nuclear forces, something that hasn’t occurred since 1972.
That was long before I was born, and I am not looking forward to living in a world without mutual constraints on its two largest nuclear arsenals.
AAS: What do we expect both countries will do?
JENNIFER KNOX: In September 2025, Russian President Putin made a surprising announcement. He publicly offered to extend the central restrictions of New START for one year following its expiration, provided that “the United States acts in a similar spirit and refrains from steps that would undermine or disrupt the existing balance of deterrence.”
What Putin didn’t acknowledge in this offer is that it represents a serious departure from Russia’s previous position on New START. In 2023, Russia suspended its participation in the treaty, arguing that strategic arms control could not be disentangled from “the conflict in Ukraine or other hostile Western actions against our country.”
This move fits a pattern of nuclear threats intended to deter US and NATO assistance to Ukraine following Russia’s full-scale invasion in 2022. However, Russia did not exercise the withdrawal clause in New START (though it could have), and it reassured the world that it would continue to adhere to the central limits of the agreement. Russia’s suspension of New START was an attempt to leverage the treaty for other political purposes, not a rejection of strategic arms control more broadly.
Now it’s up to the United States to accept an extension of New START’s limits. Shortly after Putin’s statement, US President Trump said, “It sounds like a good idea to me.” But the United States hasn’t formally responded to Russia’s proposal. Some voices close to the administration have called for the United States to use New START’s expiration as an opportunity to expand its nuclear forces, in which case the United States could put hundreds of additional nuclear weapons into launch position in a few weeks. Within a few years, US strategic forces could more than double to 3,500 nuclear weapons.
There are lots of problems with this pathway, but here’s the most obvious one: If the United States expands its strategic nuclear forces, Russia can and almost certainly will do the same. After decades of cooperative arms control, we could slide right back into a new nuclear arms race.
For the same reason that Russia couldn’t afford to hold strategic arms control hostage to other interests, the United States can’t either. After all, arms control has never relied on trust or goodwill between adversaries. Arms control is a simple matter of mutual benefit. I hope the Trump administration is wise enough to preserve those benefits.
AAS: Though New START did not constrain other nuclear states like China, how did it affect those countries’ policies?
JENNIFER KNOX: There is a huge gulf between the United States and Russia on one hand and the other seven states that possess nuclear weapons. Together, the United States and Russia possess more than 87% of the world’s nuclear weapons; the United States is estimated to have more than 3,700 warheads in its active stockpile (3,500 strategic and 200 non-strategic) while Russia has more than 4,300. By comparison, the third-largest nuclear power, China, possesses about 600.
In the past, other states haven’t been included in US–Russian strategic arms control efforts because their arsenals are so far below the limits of these agreements. But that doesn’t mean they won’t be affected by the collapse of arms control between the United States and Russia. If US and Russian arsenals expand following the expiration of New START, it may put pressure on China and other countries to expand their own nuclear forces to improve their “survivability” (the ability to retain a nuclear response capability following an attack).
AAS: What does UCS want to see happen next?
JENNIFER KNOX: Russia has offered to extend the restrictions of New START for one year following the treaty’s expiration. The United States should unequivocally accept that offer. Ideally, the United States and Russia would then use this time to negotiate a follow-on arms control agreement that would enable deeper reductions of their strategic nuclear forces, consistent with the administration’s stated desires to reduce nuclear threats. Eventually, if both countries succeed in reducing the size of their arsenals, China may be incentivized to come to the table as well—a long-stated US priority.
AAS: Are there any other opportunities for cooperation on arms control out there?
JENNIFER KNOX: Many! While most arms control efforts have stagnated, renewed US leadership could be transformational. The United States signed the Comprehensive Test Ban Treaty in 1996, but several decades later has still failed to ratify it. US ratification would be a powerful way to reinforce the norm against nuclear testing after Russia withdrew its ratification in 2023. It would also signal that the United States is committed to upholding the global taboo against testing, which has only been broken by North Korea in this century.
Another potential avenue for progress is the Fissile Material Cutoff Treaty, which would prohibit the production of highly enriched uranium and plutonium for use in nuclear weapons. This idea has been supported at various times by the Bush, Obama, Biden, and Trump administrations.
Another important arms control proposal is the effort to establish a “weapons of mass destruction–free zone” in the Middle East. The United States committed to supporting a regional conference on the establishment of such a zone in 2010, but has since reversed its position, blocking efforts for a conference to proceed.
AAS: You have been following this issue for more than 10 years. What is your personal take on the state of the international order at this moment and where do you find hope?
JENNIFER KNOX: It’s impossible to quantify the risk of nuclear war, but it’s easier to sense the direction of change. I entered the nuclear policy field in a period of energetic optimism. President Obama was the first US president to visit Hiroshima, and he delivered a passionate speech in 1992 endorsing the vision (and viability) of a world without nuclear weapons. International leaders met to trade proposals and set agendas for change.
But beneath the surface, the architecture that allows for global destruction did not change. The United States and Russia still maintained thousands of nuclear weapons, and another seven countries kept a tight grip on their own nuclear arsenals. In 2010, the United States announced a trillion-dollar modernization program to rebuild or replace nearly every component of its strategic nuclear arsenal, and the estimated cost has since doubled to around $2 trillion. Russia has used its nuclear status as a shield to terrorize its neighbors, culminating in its 2022 invasion of Ukraine. Four years later, Russia and Ukraine are still locked in a brutal war of attrition with no end in sight.
Given the risk of conflict between NATO and Russia in Europe, deteriorating conditions on the Korean peninsula, tensions in East Asia, and ongoing clashes between India and Pakistan, there is no question that the world has become a much more dangerous place. The risk of nuclear war may be as high as it has ever been. Worse, it seems like many world leaders are doubling down on dangerous and destabilizing behaviors.
I miss the easy optimism of my early career, but I still have the same hope that our future can be different from our past. After the Cold War, our fears about nuclear war faded. But the weapons didn’t go anywhere. As people turned their attention to other pressing issues, there was less public pressure on elected officials to reduce nuclear risks, and decisionmaking over nuclear weapons became concentrated in fewer hands. The world is more dangerous as a result, and it’s terrifying to live through. But the silver lining is that people are paying attention again, asking hard questions, and demanding better answers. That’s how change happens.