For decades, United States allies across the world lived with the security provided by the American nuclear umbrella, assuming there was no need to acquire their own weapons of mass destruction. However, this perception appears to be receding rapidly, as the new US National Defense Strategy for 2026 under the Presidency of Donald Trump omits explicit reference to extended nuclear deterrence, while simultaneously pressing allies to assume a larger share of their defense costs. This shift is pushing an increasing number of governments to reconsider acquiring their own nuclear weapons, raising the risk of triggering a domino effect of nuclear proliferation, analysts warn.
"Strategic autonomy" for US allies
"Allies perceive almost universally that Washington is becoming increasingly disengaged and unreliable," said Ankit Panda, a senior fellow at the Nuclear Policy Program of the Carnegie Endowment for International Peace. According to him, this evolution is leading to "different versions of strategic autonomy," as allies seek ways to bolster their own deterrent capabilities without relying exclusively on the US. The latest representative example involves South Korea, where Donald Trump ordered a reduction in joint military exercises, arguing that such drills send a message that is "completely inappropriate and hostile" toward North Korea. At the same time, early last month, the US initiated talks with South Korea regarding the peaceful use of technologies for nuclear enrichment and reprocessing. During the same period, Washington signed an agreement with Saudi Arabia to develop a civil nuclear program, which reports suggest could pave the way for domestic uranium enrichment.
France expands Europe's nuclear "umbrella"
In an effort to strengthen European independence in defense, French President Emmanuel Macron announced in March the first expansion of the French nuclear arsenal since 1992. Simultaneously, he committed to extending France's nuclear umbrella to other European Union nations within a framework dubbed "forward deterrence." Nine countries have joined the initiative, including Germany and Greece. France's move carries particular weight at a time when Europe is attempting to curb its dependence on American military protection and enhance its own defense capabilities.
Japan re-evaluates its post-war nuclear policy
In Asia, Japan is also bolstering its capabilities in nuclear defense under Prime Minister Sanae Takaichi. Her reluctance late last year to rule out a revision of Japan's three non-nuclear principles has sparked intense debate. For decades, these three principles—non-possession, non-production, and non-introduction of nuclear weapons—have served as the bedrock of the country's post-war policy. Takaichi's stance has fueled speculation that Japan could depart from its long-standing commitment to avoid any role in the deployment or development of nuclear arms. Concurrently, leadership in Lithuania and Finland, two nations bordering Russia, have moved closer toward abandoning long-held bans on hosting nuclear deployments on their soil.
The threat of a nuclear proliferation "domino effect"
None of these developments amount to an immediate decision to build a nuclear bomb. However, as Shounak Set, a researcher at the S. Rajaratnam School of International Studies in Singapore, warns, a state's efforts to enhance its security can leave adversaries feeling less secure, potentially incentivizing them to strike first. "You cannot build or deploy a nuclear deterrent without immediately raising tensions and forcing adversaries to react," stated Andrew Facini, a senior fellow at the Council on Strategic Risks. Such a development, according to Facini, could ultimately accelerate the exact security risks that a nation attempts to avoid through nuclear reinforcement.
Iran represents the most striking example
The most prominent example today is Iran, whose push to develop uranium enrichment capabilities was at least partly responsible for the current war in the Middle East. The Trump administration has repeatedly declared that "Iran cannot be allowed to acquire a nuclear weapon," while joint US and Israeli strikes in 2025 aimed primarily at preventing such an outcome. Iran is not known to possess a nuclear weapon; however, the ongoing war raises a critical question: whether military strikes against the regime have ultimately driven Tehran to make the firm decision to obtain a nuclear warhead. "We do not know whether, by attacking them, we have pushed the Iranians fully and definitively to decide to actually move forward with acquiring nuclear weapons, a decision they had not taken until now," stated Alexandra Bell, President and CEO of the Bulletin of Atomic Scientists.
New dynamics of an arms race
All nine nuclear-armed states—the US, Russia, China, the United Kingdom, France, India, Pakistan, North Korea, and Israel—continue to modernize and expand their nuclear arsenals. This trend reinforces a new arms race at a moment when escalating geopolitical tensions create a higher risk of miscalculation, according to researchers. According to a June report by the Stockholm International Peace Research Institute (SIPRI), the US and Russia remain the two dominant nuclear powers globally, jointly possessing about 83% of all operationally available nuclear warheads. "By resorting to nuclear solutions, states are creating new risks and fueling the dynamics of an arms race," stated Hans Kristensen, a senior fellow at SIPRI, in the report. He estimated that the acceleration of state efforts to acquire or reinforce nuclear capabilities is likely to undo decades of progress in limiting nuclear arsenals. "The evidence gathering indicates that nuclear-armed states are setting aside, or even abandoning, their commitments to nuclear disarmament and are instead displaying their nuclear power," Kristensen noted.
Over 12,000 nuclear warheads worldwide
Out of more than 12,000 nuclear warheads held globally, over 9,000 reside in military stockpiles for potential operational use. Approximately 4,012 warheads are estimated to be deployed on missiles and aircraft, with up to 2,200 held on high alert, meaning they could be launched within minutes. This trajectory deepens concerns that the international community is entering a new era of heightened nuclear danger.
"A more dangerous world"
A report by Carnegie last September outlined the danger in stark terms. If more nations or non-state actors acquire nuclear weapons—whether friendly states, hostile regimes, or sub-state entities—"the world will be more dangerous, both for the United States and for everyone else," it noted. "A domino effect of nuclear proliferation represents a multiplying risk," stated Andrew Facini. Every new nuclear state increases the likelihood of miscalculation, narrows decision-making windows, and could lead to "regional arms races where even conventional conflicts acquire existential dimensions." Introducing nuclear weapons into unstable regional disputes dramatically heightens the risk of unintentional escalation, Facini added.
Concerns over the Non-Proliferation Treaty
A review conference for the Non-Proliferation Treaty (NPT) held in May at United Nations headquarters failed to reach a consensus. UN Secretary-General António Guterres warned that the Non-Proliferation Treaty is undergoing erosion. The treaty entered into force in 1970 and was extended indefinitely in 1995 based on a core bargain: non-nuclear-weapon states commit not to acquire them, while nuclear powers agree to share peaceful nuclear technology and pursue disarmament.
"If we dismantle the NPT, we may never recover"
Alexandra Bell emphasized that the treaty has largely succeeded in slowing the spread of weapons of mass destruction. "Broadly speaking, the treaty has contained the tide of mass proliferation," she said. Without the safeguards provided by the NPT, more nuclear material, facilities, and technical knowledge could proliferate, increasing the threat of nuclear terrorism even from a low baseline. Bell urged Washington to reduce the incentives driving other states toward nuclear acquisition. "Building things is hard; destroying them is very easy," she warned. "If we dismantle the NPT, we may never recover from that loss of security." This warning takes on immense gravity at a time when the American nuclear umbrella is questioned more than ever by US allies themselves, while Russia, China, and other powers expand their stockpiles. The result is a vicious cycle: the more allies doubt American protection, the greater the pressure for strategic and nuclear autonomy—and as more states consider acquiring nuclear capabilities, the risk of a new global nuclear arms race surges.
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