Iran’s nuclear ambition, which is at the heart of its military conflict with the U.S. and Israel, is just one of several challenges that threaten to unravel decades of global nuclear security, scholars and practitioners said during an event at Harvard Kennedy School last week.

The discussion, moderated by Meghan O’Sullivan, director of the Belfer Center for Science and International Affairs at the School, reflected on the shifting framework of nuclear nonproliferation around the world and its critical importance to American national security, particularly as China accelerates its nuclear arms program in an effort to get on equal footing with the U.S. and Russia.

“I think there’s a very serious danger that we’re going to be in a new, probably more slow-moving but still, a new nuclear arms race competition” as a result, said Matthew Bunn, James R. Schlesinger Professor of the Practice of Energy, National Security, and Foreign Policy at HKS.

In 1963, President John F. Kennedy predicted a nightmare scenario in which perhaps 15-20 countries could have nuclear weapons by the 1970s. That panic led to the landmark Treaty on the Non-Proliferation of Nuclear Weapons. With 191 states signed on, it remains the foundational agreement that guides the use and spread of nuclear weapons and promotes disarmament around the globe. Limiting the spread of nuclear weapons, whether to adversaries or allies, remains a critical objective of U.S. national security.

“We don’t want to be in a world with 20 or 30 fingers on the nuclear button because there’s going to be much more chance that the nuclear button is going to get pressed and that the United States might be dragged into whatever takes place,” said Bunn.

That only nine countries today — the U.S., Russia, the U.K., France, China, India, Pakistan, Israel, and North Korea — are known to possess nuclear weapons is one of the “quiet successes” of global nonproliferation efforts over the last 60-plus years, panelists agreed.

But a recent Belfer Center task force and report on how the U.S. ought to approach nuclear proliferation today found broad, bipartisan consensus on the view that the steady, post-Cold War regime of treaties, institutions, and deterrence strategies has begun to break down.

In addition to the dwindling number of nuclear treaties, many of which have lapsed without replacement — including the New START treaty earlier this year — changing political attitudes have added a new hazard to nonproliferation efforts, analysts said.

The U.S. has begun warming to the notion of “allied proliferation,” in which it would be acceptable for friendly countries to have limited nuclear capabilities so they could defend themselves if attacked. It’s a view that upends decades of American policy in which non-nuclear allies had agreed to forgo weapons development in exchange for protection under the U.S. nuclear umbrella, a strategy known as “extended deterrence.” U.S. allies have grown increasingly uncertain about the credibility of that once iron-clad promise.

“There is no question Donald Trump has shaken the faith of our allies in the U.S. willingness to come forward in the terrible event that they are attacked with nuclear weapons” and to “respond with a U.S. nuclear weapon to that attack,” said Rose Gottemoeller, lecturer and research fellow at the Hoover Institution at Stanford who helped negotiate New START.

That promise, known as the extended nuclear deterrent guarantee, is a major aspect of U.S. treaty relationships with NATO, Europe, allies in Asia, Australia, and others. “So, everybody’s worried. I’m worried, to be honest,” she said.

On the other hand, she said, NATO’s capability and the physical infrastructure in Europe has “never been better,” thanks to the U.S. deployment of its most advanced warhead to Europe, the refurbishment of U.S. nuclear bases and handling facilities in Europe during the first Trump and Biden administrations, and allies’ agreement to buy F-35 fighter jets from the U.S. for nuclear missions.

To ensure the guarantee remains a strong deterrent to adversaries like Russia, Gottemoeller added, allies must “do everything they can to prove that it is an alliance that is ready to act” and that allies are well-trained and ready to participate alongside the U.S., if necessary.

Key nonproliferation institutions, like the International Atomic Energy Agency, which conducts nuclear weapons verification inspections, are becoming politicized by China, said Laura S.H. Holgate, a senior fellow at the Belfer Center who served during the Obama administration on the National Security Council and as ambassador to the IAEA from 2022 to 2025.

China, she said, has overwhelmed the IAEA with staff in a bid to leverage its development budget, “co-opt” the agency’s credibility, and advance China’s geopolitical influence and infrastructure gambit, the Belt and Road Initiative.

But there are steps the U.S. can take, outside of treaties, to ensure the past nonproliferation successes endure, the panelists said.

With a fourth generation of nuclear power reactors now under development, Holgate said now is the time to redesign them so they are both safer and less useful as a front for covert weapons-building.

Calling for the U.S. to be a more reliable partner to its allies, Bunn said the use of force to try to deter countries like Iran from developing weapons is not only “illegal,” it’s “ineffective.”

“I fear that the current war, while it has set back Iran’s nuclear capabilities somewhat, has greatly increased their motivation” to develop a nuclear weapon, Bunn said. He added that the probability Iran will have a nuclear weapon within 10 years is much greater today than it was just a year ago.

The event was the first in a new series of “convenings” by the Belfer Center named in honor of Albert Carnesale, a nuclear nonproliferation public policy specialist who spent more than two decades at the Kennedy School and mentored many of today’s top experts in the field.