The US and Russia hold nearly 90% of the world's nuclear weapons. The last treaty limiting their arsenals expires today. What's next?
The United States and Russia control about 87% of all nuclear weapons in existence globally. On Thursday, February 5, New START, the last bilateral treaty that imposed binding limits on the world's two largest nuclear arsenals, expires.
In 2025, Russia possessed approximately 5,459 nuclear warheads, and the United States 5,177/FOTO:X
The agreement, officially known as the Strategic Offensive Arms Reduction and Limitation Treaty (START III), was signed in 2010 and was the last pillar of the nuclear arms control architecture between Washington and Moscow.
According to estimates by the Federation of American Scientists, in 2025 Russia possessed about 5,459 nuclear warheads and the United States 5,177 – figures that also include decommissioned but not yet decommissioned warheads. Together, these arsenals represent nearly nine-tenths of the world total.
How nuclear arsenals were reduced
During the Cold War, the nuclear stockpiles of the two superpowers were considerably larger. In 1986, the Soviet Union had more than 40,000 warheads and the US more than 20,000, according to archival data cited by the Associated Press.
Their reduction was made possible by a series of treaties signed starting in the 1970s, amid fears generated by the Cuban Missile Crisis, which brought the world to the brink of a nuclear war.
The first major agreement was the 1972 ABM Treaty, which limited anti-missile defense systems. The United States withdrew from this treaty in 2002, citing the need to defend against emerging threats such as Iran or North Korea.
START I followed in 1991, which imposed strict limits on the number of nuclear warheads and launch vectors – ballistic missiles, bombers and submarines. The treaty expired in 2009.
A subsequent agreement, START II, signed in 1993, never entered into force after Russia did not ratify it.
What New START provided
The current treaty, New START, was signed in 2010 by US President Barack Obama and then-Russian President Dmitry Medvedev during a period of attempts to “reset” bilateral relations.
The agreement limited each party to:
-1,550 deployed strategic nuclear warheads,
-700 missiles and operational bombers,
– allowed mutual inspections, aimed at ensuring compliance with commitments.
The treaty entered into force in 2011, for a period of 10 years, being extended only once, in 2021, by the Joe Biden administration.
But, in practice, the verification mechanisms have been suspended since the COVID-19 pandemic. In 2023, Russia officially announced it was “suspending” its participation in the treaty, citing US support for Ukraine.
Why treaty expiration is important
Reuters points out that New START was the last agreement to limit weapons capable of destroying an adversary's major political, industrial and military centers. Without it, more than 50 years of formal restrictions on strategic nuclear weapons disappear.
Alexandra Bell, director of the Bulletin of the Atomic Scientists, warns that the United States and Russia are “wasting half a century of efforts to maintain nuclear stability.”
The Guardian describes the expiration of the treaty as a possible “death knell” for the global arms control regime, in a context already marked by international instability.
Is there a chance for a new deal?
The prospects for a new treaty are uncertain. Russian President Vladimir Putin suggested an informal short-term extension in 2025, but US President Donald Trump said he preferred “a better deal”.
But experts warn that a new agreement would be much more difficult to negotiate. It should include:
-missiles with medium and short range,
-new nuclear systems developed by Russia (such as the Poseidon nuclear torpedo or the Burevestnik missile),
-and possibly China, which has about 600 warheads but rejects the idea of a trilateral treaty on grounds of imbalance.
In addition, Russia has suggested including the nuclear arsenals of France and the United Kingdom — an idea rejected by NATO allies.
A trust issue
According to British analyst Sid Kaushal of the Royal United Services Institute, such an agreement requires a minimum level of trust between the parties – “a condition that is currently completely lacking”.
Reuters notes that once New START expires, both countries will theoretically have the freedom to expand their arsenals. But the process would be slow and expensive. In the long term, there are fears that the world could enter a new arms race based on the most pessimistic scenarios about the adversary's intentions.
“The expiration of the treaty does not necessarily make nuclear war more likely“, IISS expert Alexander Bollfrass told The Associated Press, “but it certainly doesn't make it any less likely.”
