The Last Nuclear Treaty Between the US and Russia Just Died

Fifty Years of Nuclear Guardrails, Gone

On February 5, 2026, the New START treaty officially expired. With it went the last legally binding agreement limiting the nuclear arsenals of the United States and Russia, the two countries that together hold roughly 90% of the world's nuclear weapons.

UN Secretary-General Antonio Guterres called it a "grave moment for international peace and security." That's not diplomatic hyperbole. For the first time since the early 1970s, there are no binding limits on the strategic nuclear forces of either country, and no new agreement is being negotiated to replace it. The framework that kept the world's two nuclear superpowers accountable to each other through decades of tension, from the Cold War through the War on Terror through the invasion of Ukraine, is simply gone.

What New START Actually Did

The treaty, originally signed in 2010 by President Obama and Russian President Medvedev, set concrete caps on both countries' nuclear capabilities. Each side was limited to 1,550 deployed strategic nuclear warheads, 700 deployed intercontinental ballistic missiles, submarine-launched ballistic missiles, and heavy bombers, and 800 total deployed and non-deployed launchers.

But the numbers were only part of the story. The real value was in the verification and transparency mechanisms: regular data exchanges, advance notifications of missile tests and deployments, and on-site inspections. These measures gave each side confidence that the other wasn't secretly building up its arsenal. That mutual visibility is what kept the nuclear competition from spiraling into worst-case-scenario planning.

Russia suspended its participation in the treaty in February 2023, shortly after the first anniversary of its full-scale invasion of Ukraine, though both sides continued to stay within the warhead limits. The suspension meant inspections stopped, but the caps remained technically in force until the expiration.

How We Got Here

The collapse of New START didn't happen overnight. It was the final chapter in a longer story of arms control unraveling.

The Anti-Ballistic Missile (ABM) Treaty was scrapped by the Bush administration in 2002. The Intermediate-Range Nuclear Forces (INF) Treaty, which had eliminated an entire class of nuclear weapons, was abandoned by the Trump administration in 2019 after the U.S. accused Russia of violations. The Open Skies Treaty, which allowed mutual surveillance flights, was withdrawn from by the U.S. in 2020.

Each treaty that fell removed a layer of transparency and predictability from the nuclear relationship. New START was the last one standing. Now it's gone too.

The Biden administration attempted to extend the treaty and begin negotiations on a replacement, but Russia's full-scale invasion of Ukraine in February 2022 effectively killed those talks. When the current Trump administration took office, Secretary of State Marco Rubio stated that any future treaty should include China, a position that Beijing has consistently rejected given that its arsenal (estimated at 500 warheads) is a fraction of what the U.S. and Russia possess (approximately 5,500 each).

The Russia Factor

On February 4, one day before the expiration, the Russian Ministry of Foreign Affairs issued a statement saying that in the absence of a formal U.S. response, Russia considered the treaty's obligations "no longer binding" and would determine its future actions based on the "evolving strategic environment." Russia did say it remains open to future diplomatic engagement "under appropriate conditions."

Russia's strategic calculus has shifted dramatically since the treaty was first signed. The war in Ukraine has consumed significant conventional military resources. Russia's economy is under severe sanctions pressure. Some analysts argue the treaty's expiration actually hurts Russia more than the U.S., since maintaining nuclear parity was one of the pillars of Russia's claim to superpower status, and without treaty frameworks, the economic burden of a nuclear arms race would fall harder on Moscow.

But others point out that Russia has been modernizing its nuclear forces regardless, investing in new delivery systems like the Sarmat ICBM and Poseidon nuclear torpedo. Without verification mechanisms, neither side will have clear visibility into what the other is actually doing, which creates the conditions for miscalculation.

Why This Matters for Everyone

The immediate concern isn't that the U.S. or Russia will start mass-producing warheads next week. Both countries have the industrial capacity to expand their arsenals, but doing so takes time and enormous resources.

The bigger risk is structural. Without binding limits, both countries will plan for worst-case scenarios. Military planners on each side will assume the other might be building up, which creates pressure to build up in response. This dynamic, the classic security dilemma, is exactly what arms control treaties were designed to prevent.

There's also the global proliferation risk. If the world's two largest nuclear powers can't agree to limit their own arsenals, the argument for restraint by other countries becomes much weaker. China is already expanding its nuclear capabilities. India, Pakistan, and North Korea are modernizing theirs. A world without U.S.-Russia arms control doesn't just affect those two countries; it signals to every nuclear-armed state that the era of negotiated limits may be over.

What Comes Next

Right now, there's no clear path to a replacement treaty. The U.S. insistence on including China makes negotiations significantly more complex. China has shown no interest in joining a trilateral framework, and some experts argue it's unreasonable to expect China to negotiate caps when its arsenal is roughly one-tenth the size of America's or Russia's.

The Munich Security Conference, which wrapped up on February 15, highlighted the broader dysfunction. Secretary Rubio met with Zelensky on the sidelines, but the conference's discussions underscored how fractured the transatlantic relationship has become under the current Trump administration. European leaders are increasingly focused on building their own defense capabilities rather than relying on American commitments, a trend that extends to nuclear deterrence.

The most realistic near-term scenario may not be a new treaty at all, but rather informal agreements or unilateral declarations of restraint. Some arms control experts have proposed a framework of "mutual transparency measures" that would be politically easier to achieve than a formal treaty but still provide some of the verification benefits that New START offered.

Whatever happens, the world just became a measurably more dangerous place. The guardrails that prevented the nuclear competition from running off the rails for over half a century are gone, and nothing has replaced them.