US And Russia Enter New Nuclear Era As Treaty Ends

For the first time in more than half a century, there are no formal limits on the world’s two largest nuclear arsenals. At midnight on February 5, 2026, the New START treaty—the last remaining nuclear arms control agreement between the United States and Russia—expired, ushering in a period of uncertainty and heightened risk that experts warn could spark a new arms race and further destabilize global security.

The New START treaty, signed in Prague on April 8, 2010, by U.S. President Barack Obama and Russian President Dmitry Medvedev, was a cornerstone of post-Cold War arms control. According to swissinfo.ch, the accord capped each nation at 1,550 deployed strategic nuclear warheads and 700 delivery systems, including submarine-launched and intercontinental ballistic missiles and heavy bombers. It also allowed for 18 short-notice, on-site inspections annually and required both sides to exchange data twice a year, fostering a degree of transparency that many experts now say is sorely lacking.

"It is disturbing to see that this treaty will expire without any agreement on its replacement," said Alicia Sanders-Zakre, Head of Political Affairs at the International Campaign for the Abolition of Nuclear Weapons (ICAN), in an interview with swissinfo.ch. She warned, "A new nuclear arms race between the US and Russia would only add to the level of risk that is already unacceptable today."

The New START treaty was the last in a series of agreements designed to reduce the massive Cold War-era nuclear arsenals of the U.S. and Russia, which together still possess about 90% of the world’s 12,000 nuclear warheads, according to the Stockholm International Peace Research Institute (SIPRI). Its expiration marks the end of an era of bilateral arms control that began with the Strategic Arms Limitation Talks (SALT) in the early 1970s and continued through the original START treaty signed in 1991 by U.S. President George H. W. Bush and Soviet leader Mikhail Gorbachev.

The demise of New START is not a surprise to close observers. The treaty’s inspection regime broke down during the COVID-19 pandemic, and efforts to resume verification collapsed amid Russia’s 2022 invasion of Ukraine and the subsequent deterioration in U.S.-Russia relations. In February 2023, Russia suspended its participation in the treaty, citing U.S. support for Ukraine. Despite these setbacks, both sides had, until now, largely adhered to the treaty’s limits.

Notably, Russian President Vladimir Putin floated the idea of voluntarily respecting the treaty’s ceilings for an additional year in September 2025, but the United States did not offer an official response. Former U.S. President Donald Trump, who had previously expressed reservations about letting the treaty lapse, told The New York Times earlier this year, "If it expires, it expires. We’ll do a better agreement." Trump has argued that any future treaty should include China, whose rapidly expanding nuclear arsenal is a growing concern for Washington.

China’s nuclear buildup adds a new layer of complexity to arms control efforts. According to SIPRI, China now possesses an estimated 600 nuclear warheads, with production accelerating at roughly 100 warheads per year since 2023. While this is still a fraction of the U.S. and Russian arsenals, the Pentagon’s 2025 report on Chinese military capabilities warned of a "growing" and increasingly sophisticated force. Beijing, for its part, has insisted that the major nuclear powers must first reduce their own stockpiles before expecting China to join any multilateral arms control negotiations.

Paul van Hooft, a researcher at the U.S. think tank Rand, told El País by email that, "The main advantage of Cold War-era arms control talks is that they generated institutionalized knowledge in both the United States and Russia about the other side." Without the verification and communication mechanisms that New START provided, the risk of miscalculation rises. "Without transparency, each side will assume the worst-case scenario, and that definitely won’t contribute to greater trust," explained Pavel Podvig, director of the Geneva-based Russian Nuclear Forces Project, in a phone interview with El País.

The treaty’s expiration has already had symbolic repercussions. On January 27, 2026, the Bulletin of the Atomic Scientists moved its famous Doomsday Clock to just 85 seconds before midnight—the closest it has ever been to symbolic global catastrophe. The organization cited, among other factors, the collapse of the last U.S.-Russia arms control agreement and the ongoing modernization of nuclear arsenals worldwide.

The potential consequences of a world without arms control are sobering. As SIPRI researcher Tytti Erästö told El País, "The qualitative arms race has been underway for quite some time, and without regulation, a numerical arms race is also possible." The end of New START removes the only formal check on the size and readiness of the world’s largest nuclear stockpiles, at a time when both the U.S. and Russia are already engaged in modernizing their arsenals and developing new delivery systems.

Some experts believe that, at least in the short term, both sides may continue to respect the treaty’s limits out of inertia or self-interest. "It is likely that both sides will respect the treaty to a greater or lesser extent as if it were still in force, at least for now, since that would cause the least disruption," Van Hooft suggested to El País. However, without inspections and data exchanges, mutual suspicion is likely to grow.

This is the first time since 1972 that the U.S. and Russia have no agreement limiting their strategic nuclear weapons. While both remain parties to the 1968 Treaty on the Non-Proliferation of Nuclear Weapons (NPT), the NPT lacks the concrete verification and reduction mechanisms that made New START effective. The 2017 Treaty on the Prohibition of Nuclear Weapons (TPNW), which bans the development and possession of nuclear arms, has been signed by around 100 countries, but none of the major nuclear powers or their key allies have adopted it. As Sanders-Zakre of ICAN told swissinfo.ch, "As long as there is just one nuclear weapon left, the risk still exists that it could be used. The only guarantee is therefore to eliminate all of them, and that is why TPNW is so important."

With the war in Ukraine ongoing and tensions between major powers on the rise, the prospects for a new arms control agreement appear bleak. Moscow has signaled that it wants any future deal to include the United Kingdom and France, while Washington insists on bringing China to the table. As things stand, no trilateral or multilateral agreement seems likely in the short or medium term.

For now, the world faces an era of renewed uncertainty, as the last guardrails on the most destructive weapons ever invented fall away. The stakes, as the Doomsday Clock reminds us, have rarely been higher.