The end of New START: Why the last US-Russia nuclear treaty mattered

The last nuclear treaty between the United States and Russia, the New START agreement, ended on Thursday, lifting restrictions on the nuclear arsenals of both powers.

The development has triggered fears of a new global arms race, with the US and Russia together controlling more than 80 per cent of the world’s nuclear warheads.

What was the New START agreement?

The New START, or Strategic Arms Reduction Treaty, was signed in 2010 in Prague by then US President Barack Obama and then Russian President Dmitry Medvedev, as a successor to the original START I (1994-2009). The new treaty went into effect in 2011. The agreement limited each country’s nuclear arsenal to 1,550 deployed strategic warheads — a reduction of nearly 30 per cent from the previous limit set in 2002.

The limits applied to long-range nuclear warheads on delivery systems ranging from ground-launched intercontinental ballistic missiles (ICBMs) and submarine-launched ballistic missiles (SLBMs) to strategic bombers.

Why did the New START end?

Under the presidency of Joe Biden, the US in February 2021 agreed with Russia to extend New START for five years. Subsequently, tensions between Washington and Moscow spiked with the war in Ukraine. After winning a second term, US President Donald Trump did not follow up on a proposal by Russian President Vladimir Putin, made in September 2025, to extend the treaty’s limits for one year. Trump has also called for nuclear testing to resume after a long moratorium, although this has not yet been operationalised.

Why did the treaty matter?

The New START ensured verifiable limits on ICBMs, SLBMs and heavy bombers, and included substantial inspection and notification mechanisms for both nations. The treaty’s limitations on strategic nuclear weapons stockpiles were seen as providing time and space for both countries to explore new, verifiable arms control arrangements that could further reduce risks. 

What are the implications of its end?

There are concerns that the collapse of the treaty could mark a major blow to over five decades of arms control efforts, particularly at a time of heightened global tensions and a lowering of thresholds for the use of force — including the potential deployment of strategic weapons. The development is particularly significant as the 1970 Nuclear Non-Proliferation Treaty (NPT) is also due for review this year.

Under the NPT framework, non-nuclear-weapon states committed to refraining from acquiring such arms in return for assurances that nuclear-armed states would pursue disarmament in good faith.

United Nations Secretary-General António Guterres described the expiry of the New START as a “grave moment for international peace and security”, and urged the US and Russia “to return to the negotiating table without delay and to agree upon a successor framework”.

“For the first time in more than half a century, we face a world without any binding limits on the strategic nuclear arsenals of … the two states that possess the overwhelming majority of the global stockpile of nuclear weapons,” Guterres said in a statement. 

“This dissolution of decades of achievement could not come at a worse time — the risk of a nuclear weapon being used is the highest in decades,” he added.