Fraying U.S. Nuclear Umbrella Pushes Allies Toward Proliferation

Iran is the test case. The Trump administration has repeatedly said Iran cannot be allowed to have a nuclear weapon, and the joint U.S.-Israeli strikes in 2025 were aimed at that objective. Iran is not known to possess a weapon. The attacks may have pushed Tehran toward a decision it had not made, said Alexandra Bell, president and CEO of the Bulletin of the Atomic Scientists. "We don't know if by the act of attacking them we have pushed the Iranians, fully and finally, to decide to actually go nuclear, which is a decision they had not made as of yet."

All nine nuclear-armed states have continued to modernize and expand their arsenals, fueling an arms race that researchers say carries a new risk of miscalculation. Russia and the U.S. together hold about 83% of usable warheads, according to a June report from the Stockholm International Peace Research Institute. "By reaching for nuclear solutions, states are creating new risks and fueling arms-race dynamics," Hans Kristensen, a senior fellow at the institute, said in the report.

Of the more than 12,000 warheads held by nuclear powers, more than 9,000 sit in military stockpiles for potential use. An estimated 4,012 are deployed with missiles and aircraft; up to 2,200 remain on high alert, launchable within minutes.

"The evidence is growing that the nuclear weapon states are sidelining, and even walking away from, their disarmament commitments and are instead flexing their nuclear muscles," Kristensen said.

A Carnegie Endowment report in September warned that with more nuclear-armed states, "the world will be a more dangerous place, for the United States and for everyone else."

"A proliferation cascade is a compounding risk," Facini said. Every new nuclear state multiplies the chances for miscalculation and shrinks decision-making windows, potentially sparking regional arms races where even conventional clashes carry existential stakes.

The treaty meant to stop that cascade is under strain. A review conference at United Nations headquarters in May failed to reach consensus, and UN Secretary-General Antonio Guterres warned that the Nuclear Non-Proliferation Treaty is "eroding." The pact, in force since 1970 and extended indefinitely in 1995, rests on a central bargain. Non-nuclear states agree never to acquire weapons, and nuclear states share peaceful nuclear technology and pursue disarmament.

The treaty has "by and large stemmed the flow of mass proliferation," Bell said. Without its safeguards, more nuclear material and expertise would be in circulation, raising the risk of nuclear terrorism, albeit from a low base.

Bell urged Washington to reduce the incentives for other states to acquire weapons. "Building things is hard. Breaking things is very easy," she said. "If we break the NPT, we may never recover from that lapse in security."