Unraveling of US umbrella raises risk of nuclear explosion

For decades, allies around the world rested in the comfort of the United States’ nuclear umbrella, confident that their own weapons of mass destruction were not needed.

That belief is rapidly disappearing after President Donald Trump’s latest 2026 National Defense Strategy removed explicit mention of extended deterrence, pressuring allies to spend more of their own money on national defense.

The changes are causing more governments to reconsider whether to acquire their own nuclear weapons, raising the risk of a proliferation cascade, analysts say.

Ankit Panda, a senior fellow in the Nuclear Policy Program at the Carnegie Endowment for International Peace, said allies almost universally perceive Washington as becoming more “indifferent and less reliable” and encouraging “various forms of strategic autonomy.”

Most recently, US President Donald Trump ordered a curtailment of joint military exercises with ally South Korea, saying they were sending a “totally inappropriate and hostile” signal to North Korea.

Early last month, the United States began talks on South Korea’s peaceful enrichment and reprocessing and signed a Saudi civilian nuclear deal that reportedly could pave the way for domestic enrichment.

Aiming to strengthen Europe’s independence, French President Emmanuel Macron in March announced the first increase in warheads since 1992 and pledged to extend the nuclear umbrella to other countries in the region under a so-called “forward deterrence” partnership. Nine countries, including Germany and Greece, participated in the initiative.

Japan is also stepping up efforts in the field of nuclear defense under Prime Minister Sanae Takaichi. Late last year, Prime Minister Sanae Takaichi came under scrutiny for her reluctance to reject a review of Japan’s three non-nuclear principles, fueling speculation that she would reverse her decades-old pledge not to play any role in deploying nuclear weapons.

Leaders of Lithuania and Finland, which border Russia, are moving closer to scrapping a long-standing ban on deploying nuclear weapons in their countries.

While none of these developments would lead to a decision to build a bomb, a state’s efforts to tighten security could make an adversary feel less safe and prompt a pre-emptive strike, said Shonak Set, a research fellow at the S. Rajaratnam School of International Studies in Singapore.

“You cannot build or deploy a nuclear deterrent without immediately escalating tensions and forcing an adversary to respond,” said Andrew Fasini, a senior fellow at the Strategic Risk Council, which could accelerate the security risks that proliferating states are trying to avoid.

The defense ministries of the United States and Japan, as well as the European Union’s foreign affairs agency, the European External Action Service, did not respond to CNBC’s requests for comment.

The best example is Iran, whose pursuit of enriched uranium is, at least in part, the cause of the current Middle East wars. The Trump administration has repeatedly asserted that “Iran cannot be allowed to possess nuclear weapons,” and the joint U.S.-Israel attack in 2025 was aimed at that goal.

Iran is not known to have nuclear weapons, but with the war, “I don’t know if by the act of attacking Iran we forced the Iranians to make a full and final decision to actually go nuclear, which they had not yet decided to do,” said Alexandra Bell, president and CEO of the Bulletin of the Atomic Scientists.

The nine nuclear powers – the US, Russia, China, Britain, France, India, Pakistan, North Korea and Israel – all continue to modernize and expand their arsenals, leading to an escalating arms race amid rising tensions and researchers say there is a “risk of new miscalculations”.

According to a June report from the Stockholm International Peace Research Institute, Russia and the United States remain the dominant nuclear powers, possessing about 83% of usable nuclear warheads. “By reaching for a nuclear solution, countries are creating new risks and accelerating the dynamics of an arms race,” Hans Christensen, a senior researcher at the company, said in the report.

He added that decades of demobilization efforts are likely to be reversed in the coming years as countries accelerate their pursuit of nuclear weapons.

“There is growing evidence that nuclear-weapon states are sidelining and even moving away from their commitments to disarmament, and are instead flexing their nuclear muscle,” Christensen said.

Of the more than 12,000 nuclear warheads possessed by nuclear-weapon states, more than 9,000 are in military stockpiles for possible use. An estimated 4,012 warheads are deployed along with missiles and aircraft, and up to 2,200 are on high alert and could be launched within minutes.

Last September’s Carnegie Report put it bluntly: “The world will become a more dangerous place for the United States and everyone else as more actors acquire them, whether friendly or unfriendly or subnational groups.”

“A cascade of nuclear proliferation increases the risks,” Facini said, adding that each new nuclear state increases the chance of miscalculation, narrows the framework for decision-making and could trigger “an existential regional arms race.”

Facini added that introducing nuclear weapons into volatile regional conflicts greatly increases the risk of unintended escalation.

A new review round held at UN headquarters in May failed to reach an agreement, with UN Secretary-General António Guterres warning that the Treaty on the Non-Proliferation of Nuclear Weapons was “eroding”.

The treaty, which entered into force in 1970 and was extended indefinitely in 1995, provides a central agreement between nuclear-weapon states to share the benefits of peaceful nuclear technology and pursue nuclear disarmament, while non-nuclear states agree never to acquire nuclear weapons.

Bell said the treaty “has largely stemmed the tide of mass proliferation.” Without these safeguards, more nuclear material, facilities and expertise would be in circulation, increasing the risk of nuclear terrorism, even at low levels, she said.

Mr. Bell called on Washington to reduce incentives for other countries to acquire nuclear weapons. “It’s hard to build things. It’s very easy to destroy things,” she says. “If we break the NPT, we may never recover from the loss of security.”