Nuclear treaty that kept world peace just expired: What happens now?

Washington DC — A cornerstone of global nuclear restraint has quietly fallen away.

With the expiry of the New START treaty earlier this month, the United States and Russia have entered unfamiliar territory, with no binding caps, no verified limits, and rising uncertainty over how the world’s two largest nuclear powers will manage their arsenals in the years ahead.

Noted political analyst Dr Stephen J. Farnsworth, Professor of Political Science at the University of Mary Washington, told TRT World, “The expiration of the treaty may lead to a dangerous and expensive expansion of the nuclear arsenals of Russia and the US.”

The New START treaty, signed in 2010 by Presidents Barack Obama and Russia’s Dmitry Medvedev, capped each side at 1,550 deployed strategic nuclear warheads on up to 700 delivery systems, intercontinental ballistic missiles, submarine-launched missiles, and heavy bombers.

It included mechanisms for on-site inspections, regular data exchanges, and notifications that increased transparency and reduced the risk of deadly miscalculation.

These measures helped stabilise US-Russia relations after the Cold War, when earlier pacts like START I began reducing vast stockpiles.

The treaty entered into force in 2011 and was extended in 2021 for five years, running until February 5, 2026. Inspections halted during the COVID-19 pandemic and never resumed.

Voluntary limits continue

Russia suspended participation in 2023 amid tensions over Ukraine, though it said it would respect the numerical caps until expiration.

With the pact now lapsed, the US and Russia, which together hold nearly 90 percent of global nuclear warheads, more than 10,500 combined, face no binding restraints on deployments or modernisation.

China adds further complexity. Its arsenal, estimated at around 600 warheads, is growing by roughly 100 annually and could exceed 1,000 by 2030.

The expiration follows failed diplomacy.

In 2025, Russian President Vladimir Putin offered to voluntarily observe New START limits for another year if the US reciprocated, warning that a lapse could destabilise global security and spur proliferation.

US President Donald Trump rejected the proposal, calling New START a “badly negotiated deal” and insisting on a “new, improved, and modernised” treaty that includes China.

Beijing has rejected that condition, citing its smaller arsenal and urging bilateral US-Russia talks instead.

Russia says it will continue to observe the limits set under the recently-expired New START nuclear arms reduction treaty if the US does the same, Russian Foreign Minister Sergey Lavrov said on Wednesday.

"We proceed from the fact that this moratorium, on our part, which was announced by our president, will remain in effect, but only as long as the United States does not exceed the aforementioned limits," Lavrov said, addressing the lower house of Russia's parliament. 

Lavrov described personal relations between Putin and Trump as "excellent," saying that their "mutual sympathy and respect helped create the atmosphere that allowed them to reach understanding" on specific issues during their August summit in Anchorage, Alaska.

He emphasised that while the Kremlin hasn't yet launched a "strategic dialogue" with the Trump administration, "we are always open for such dialogue."

Wider ripple effects

Kremlin spokesperson Dmitry Peskov also said last week that Russia would "retain its responsible, thorough approach to stability when it comes to nuclear weapons."

Even without treaty limits, both powers retain monitoring capabilities through satellites and intelligence systems. The absence of verified data sharing, however, raises the risk of misperception in an already low-trust climate.

A White House official told the US news network CBS News that Trump would decide the future course on nuclear arms control, adding he would clarify it "which he will clarify on his own timeline."

The end of New START closes a chapter that began with the 1972 SALT I agreement, when sustained dialogue gradually reduced arsenals from Cold War peaks.

Attention may now shift towards qualitative advances, more precise, survivable, or hypersonic systems, rather than sheer numbers.

Without renewed engagement among nuclear powers, experts fear a return to unchecked competition that could unsettle global stability for decades.

Farnsworth stressed the wider ripple effects, noting that “European nations and China, which were not part of the agreement, benefitted from the decades of reduced nuclear tensions between the US and Russia and before that the Soviet Union, when this treaty and others that existed earlier on were in place.”

He warned that “these nations may choose to expand their own nuclear arsenals in response to the greater international uncertainty that follows the end of the treaty.”