The New Strategic Arms Reduction Treaty, known as New START, is the last remaining nuclear arms control agreement between the United States and Russia. Its expiry marks a critical moment in global security, potentially ending more than five decades of formal limits on the world’s two largest nuclear arsenals. With no replacement treaty in place and relations between Washington and Moscow at a low point, the treaty’s expiration raises fears of renewed nuclear competition at a time of heightened global instability.
Origins of the Treaty
New START was signed in 2010 by U.S. President Barack Obama and then-Russian President Dmitry Medvedev, a close ally of Vladimir Putin, during a period when relations between the two countries were undergoing a diplomatic “reset.” The treaty entered into force in 2011 and was designed to curb the most destructive category of nuclear weapons: long-range strategic arms capable of striking major political, military, and industrial targets.
Under the agreement, each side was limited to 1,550 deployed strategic nuclear warheads. It also capped the number of deployed intercontinental ballistic missiles, submarine-launched ballistic missiles, and heavy bombers at 700, with a total of 800 launchers allowed.
How Compliance Was Enforced
A key pillar of New START was its verification regime. The treaty allowed for short-notice, on-site inspections, enabling each side to confirm the other’s compliance and reducing the risk of miscalculation or mistrust.
This system effectively broke down in recent years. Inspections were first suspended during the COVID-19 pandemic and later halted entirely in 2023 after President Putin suspended Russia’s participation in the treaty, citing U.S. support for Ukraine. Since then, both sides have relied on their own intelligence assessments. Despite this, Washington and Moscow have said they continued to observe the treaty’s numerical limits until its expiry.
Why the Treaty Cannot Simply Be Extended
The New START treaty includes a provision allowing for only one extension, which was exercised in 2021 shortly after Joe Biden took office as U.S. president. With the treaty now expiring, no further formal extension is possible under its terms.
In September last year, Putin proposed an informal agreement in which both sides would voluntarily adhere to the warhead limits for another year. As of the treaty’s final day, U.S. President Donald Trump had not responded to the proposal.
In the United States, the idea has split opinion. Supporters argue that an informal extension would signal restraint and buy time to negotiate a successor agreement. Critics contend that remaining bound by the limits would prevent the U.S. from responding to China’s rapid nuclear build-up and could be interpreted as strategic weakness.
Why the Expiry Matters
If the United States and Russia stop observing mutual limits on their strategic nuclear arsenals, it would bring an end to decades of structured arms control dating back to the Cold War. The expiration of New START leaves a regulatory vacuum, with no ongoing negotiations for a successor treaty.
Arms control advocates warn that the absence of a treaty increases nuclear risks, particularly amid wars in Ukraine and the Middle East. Beyond numerical caps, treaties provide transparency and predictability, reducing the chance that arms races spiral based on worst-case assumptions.
What Happens Without a Treaty
Without New START, both countries would be legally free to increase the number of missiles and deploy hundreds of additional strategic warheads. Experts caution, however, that such expansions would not be immediate. Technical, logistical, and financial constraints mean it would take at least many months, if not longer, to significantly increase deployed arsenals.
The greater concern lies in the longer term. Without agreed limits or verification mechanisms, both sides could feel compelled to expand their arsenals continuously in response to perceived threats, creating an unregulated and potentially destabilising arms race.
Prospects for a Replacement Agreement
President Trump has said he wants a new and improved nuclear treaty, but experts argue that negotiating a successor to New START would be complex and time-consuming. Any new agreement would likely need to address categories of weapons not covered by New START, including short- and intermediate-range nuclear weapons, as well as newer Russian systems such as the Burevestnik nuclear-powered cruise missile and the Poseidon nuclear torpedo.
There is also no consensus on who should participate. Trump has expressed a desire for a trilateral agreement involving China, but Beijing rejects this idea, arguing that its nuclear arsenal is far smaller than those of the United States and Russia. Moscow, meanwhile, says any talks should also include the nuclear forces of Britain and France, a proposal those countries oppose.
Analysis
The expiry of New START represents more than the end of a treaty; it signals the collapse of a shared framework for managing existential risk between rival powers. Even at the height of Cold War hostility, arms control agreements served as guardrails against catastrophe. Their erosion reflects a world in which strategic mistrust now outweighs cooperative restraint.
What makes this moment particularly dangerous is the absence of dialogue. Without talks, transparency, or verification, nuclear policy becomes driven by suspicion rather than evidence. While a sudden arms surge is unlikely, the gradual return to worst-case planning could entrench a new arms race that is harder to reverse than to prevent. In that sense, the true cost of New START’s expiry may not be measured in warheads, but in the loss of predictability and trust that once helped keep nuclear competition in check.
With information from Reuters.
