As START ends, nuclear risks and proliferation will rise

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“If it expires, it expires. We’ll do a better agreement,” remarked US President Donald Trump, when asked about the expiry of the last existing nuclear arms control agreement between the United States and Russia. The New START (strategic arms reduction treaty) expires on the 5th of February, making 2026 the first time in several decades that there is no bilateral agreement on nuclear arms control between the world's two biggest nuclear powers.

There is no successor agreement in sight, and despite President Trump’s comment to the New York Times, there is little indication that China would want to be party to such a treaty. In September 2025, Russian President Vladimir Putin expressed interest in extending the limits of New START for a year, however, the US has not formally responded to this. Given these realities, as the deadline approaches, there is much uncertainty, and much hanging in the balance.

How START worked

New START’s contributions to the relative stability that has persisted for the 15 years since it has come into force, lie in both the central numerical limits it imposes, as well as verification protocols. The treaty limits deployed warheads on both sides to 1550, including warheads on ballistic missiles, deployed delivery vehicles to 700, and limits launchers such as silos, bombers and submarine tubes to 800.

It mandates that both countries meet these central limits. Compliance is verified through mechanisms including annual on-site inspections, data exchanges twice a year, mandatory notifications about any movement or change to missiles or launchers, and unique IDs through which individual bombers and launchers can be tracked.

Attempts to weaponise START

These measures have allowed the two countries to manage their competition for the last decade-and-a-half. However, the treaty is under severe pressure. Both Russia’s invasion of Ukraine in 2022, and China’s growing nuclear arsenal have added pressure on the US. Russia also suspended notifications and data exchanges in 2023, merely two years after the five-year extension of New START. Putin used New START as leverage, to try and get the US to cut off support for Ukraine.

Since the inking of New START, both countries’ capabilities have also evolved. In 2022, the US criticised Russia’s sabre-rattling and expressed interest in limiting newer Russian systems, including theatre-range weapons. In the past, according to RUSI, Russia also expressed interest in restricting US ballistic missiles and non-nuclear long-range delivery systems as well.

A future treaty cannot ignore China

Meanwhile, China has quietly been building its nuclear arsenal. In its 2025 Victory Day Parade, China displayed some of these capabilities. While China only has 600 warheads according to SIPRI, it has a diverse assortment of delivery systems and the Pentagon estimates that it will also have close to 1000 warheads by 2030.

Although some reports have suggested that trilateral arms control is the need of the hour, China has expressed no willingness to participate in any such treaty. Late last year, China released a white paper on arms control– the first in 20 years– and used it to spell out in no uncertain terms that it has no interest in participating in a multilateral nuclear arms control treaty, unless the countries with the biggest arsenals initiate the process. China also used the paper to frame the global nuclear buildup as an outcome of American actions, which suggests that it is unlikely to curb its own growth unless the Trump administration commits to doing the same.

So far, neither party has formally committed to extending compliance with New START’s limits until a successor agreement is signed. Although Putin suggested doing this last year, the US has not formally agreed, and time is running out.

Consequences of a world without a nuclear treaty

What do all these various threads mean? Amidst all the uncertainty, a few things are clear. Firstly, in the absence of data sharing, both the US and Russia will have to rely on intelligence and assumptions. In the absence of New START, if any disputes do arise, the Bilateral Consultative Commission, which was designed to be the formal channel for resolving compliance issues, will also be dissolved.

In the longer term, there is a chance that any trilateral agreement will get stuck before it begins. Given that China’s arsenal is significantly smaller than the US’ and Russia’s, China has no incentive to commit to curbing its own growth unless it reaches parity. There’s more widespread effect that is likely to emerge if the US and Russia abandon their limits. If the US, Russia, and China are seen as actively developing their arsenals, non-nuclear states could potentially feel justified in finally pursuing their own nuclear ambitions.

These worst-case scenarios aside, there is still a silver lining that lies in both Trump's and Putin’s statements that indicate a willingness to eventually maintain limits and perhaps ink an updated agreement. If an interim agreement to adhere to New START’s limits is signed, it will still benefit from a verification mechanism. Until then, there will be no formal constraints on the superpowers’ nuclear arsenals.