CHATHAM HOUSE The Iran war risks triggering a new wave of nuclear proliferation States may be tempted to pursue their own nuclear weapons as they seek deterrence against attacks amid uncertainty over US guarantees. Expert comment Published 30 March 2026

 CHATHAM  HOUSE

The Iran war risks triggering a new wave of nuclear proliferation

States may be tempted to pursue their own nuclear weapons as they seek deterrence against attacks amid uncertainty over US guarantees.

Expert comment

Published 30 March 2026 —

4 minute READ

Image — A man in the South Korean capital Seoul watches a television screen showing a news broadcast with file footage of a North Korean missile test on 12 September 2024. Photo by JUNG YEON-JE/AFP via Getty Images.

Georgia Cole

Research Associate, International Security Programme

The US-Israeli war with Iran is taking place as the global non-proliferation regime is already under significant strain. 

New START, the last bilateral nuclear arms control treaty between the US and Russia, expired in February with nothing to replace it. China is currently expanding and modernizing its nuclear arsenal. France has announced an expansion of its nuclear programme and closer cooperation with European partners. 

Public opinion in several non-nuclear states such as Turkey, Poland and South Korea seems to be shifting towards support for developing domestic nuclear capabilities, as the lessons of the Cold War and the devastating consequences of nuclear weapons fade from living memory. 

This comes amid rising doubts over Washington’s ability to uphold its extended deterrence and security commitments to allies. In particular, the US’s reported redeployment of part of its THAAD missile defence systems from South Korea to the Middle East may be cause for concern among US allies in East Asia.

The strains on the non-proliferation regime predate the Iran war and the reported THAAD redeployment. But they risk fracturing the regime at precisely the moment when the international community can least afford it.

A dangerous lesson

There is a danger that many states watching these developments will absorb a straightforward message: nuclear weapons deter attack in a way that conventional capabilities cannot. 

This belief was already gaining ground after Russia’s invasion of Ukraine, which some have interpreted as confirmation that Kyiv relinquishing its Soviet-era arsenal left it exposed. While establishing an independent Ukrainian nuclear deterrent would have faced profound practical obstacles, including questions of operability and command and control, it seems unlikely that Russia would have launched a full-scale invasion if Ukraine had nuclear weapons. 

Likewise, Iraq and Libya, which abandoned their weapons programmes, were also targeted with military action. In contrast, North Korea, which has developed nuclear weapons, has so far avoided military action against it. 

The US and Israel have justified their strikes on Iran in part as aimed at preventing Tehran from developing a nuclear weapon in future. However, observers may take the lesson that Iran would not have been attacked if it had a nuclear deterrent already.

Besides, Iran was also attacked during two active rounds of negotiations – in June 2025, and again in late February 2026. For states weighing whether to engage diplomatically with Washington, that precedent is significant. Dialogue did not protect Iran. 

Proliferation in the Middle East

Since the war, prominent voices within the Iranian regime are now arguing that Tehran should quit the NPT and develop the bomb, according to Reuters. 

Iran’s new supreme leader, Mojtaba Khamenei, is reported to be more hardline than his father and predecessor, who issued a fatwa against nuclear weapons and reportedly pushed back against senior Iranian military leaders who argued for the bomb. 

If Iran were to develop a nuclear weapons programme, the consequences for regional proliferation could be severe. 

Saudi Arabia’s Crown Prince Mohammed bin Salman has repeatedly stated his opposition to nuclear weapons but has previously warned, including in a 2023 interview, that the kingdom would seek to acquire a nuclear weapon if Iran does. This could in turn prompt even wider proliferation in an already volatile region.

East Asia

In East Asia, the picture is similarly concerning. In Japan and South Korea, serious debates about domestic nuclear acquisition have been building for several years. These are driven by China’s sustained nuclear buildup, North Korea’s expanding arsenal and concerns about the reliability of US security guarantees.

The US stationing THAAD missile defence systems in South Korea in 2017 was a visible symbol of its commitment to the region. It reinforced Washington’s commitment to extended deterrence – to defend its allies if they are attacked, including potentially by using its nuclear weapons. 

Washington remains committed to defending South Korea under their 1953 Mutual Defense Treaty and retains a strong military presence in East Asia. 

Philippine Navy sailors hold a Japanese flag in front of a Hyuga-class helicopter destroyer of the Japan Maritime Self-Defense Force, in Manila on 21 June 2025. (

Related work

The Iran war should boost security cooperation by US Pacific allies like Japan, the Philippines and South Korea

 

But the reported THAAD redeployment signals that Washington may be prioritizing Middle Eastern engagements over its Indo-Pacific commitments.  This exposes the limits of US capacity across multiple fronts simultaneously, and risks leaving Washington’s partners exposed to opportunistic attacks while the US is distracted elsewhere. 

The Iran war has also sparked questions over the US’s ability to defend its allies. While US defences have shot down many Iranian missiles, Washington has been unable to fully shield its partners in the Middle East from Iran’s retaliatory strikes.

In this context, non-nuclear US partners may seek to develop their own domestic nuclear deterrence capabilities.

Restating the case against proliferation 

None of this makes proliferation inevitable, or strategically rational. The potential costs of pursuing a nuclear weapon remain severe: comprehensive sanctions, exclusion from international financial systems and the collapse of security and trade relationships that took decades to build.

Extended deterrence, when credible, continues to offer a more reliable guarantee than an emerging and vulnerable domestic programme. The path to nuclear deterrence is neither quick nor cost-free – in the interim, a state acquiring a weapon is more likely to attract pre-emptive action than to deter it. 

The problem is that these arguments have been undermined and even contradicted. The expiry of New START has weakened the case for restraint elsewhere.  Last month, the US accused Russia and China of conducting nuclear tests, after US President Donald Trump instructed the Pentagon to restart testing for the first time in 30 years. And while Trump has previously described proliferation as the world’s ‘biggest problem’, in the same 2016 interview he did not rule out Japan and South Korea acquiring their own weapons and said it was ‘something we have to talk about.’  

This ambiguity, combined with the signals from recent events, risks normalizing what has long been treated as a fundamental red line. Restoring the credibility of the non-proliferation norm requires action on several fronts, and urgently.

Averting proliferation risks

Washington must prioritize shoring up its extended deterrence commitments to East Asian allies. Visible reassurance – through deployments, joint exercises and formal reaffirmations – matters as much as underlying capability. US allies need to see that the reported THAAD withdrawal was an operational decision rather than a signal of diminishing commitment, and that the gap it has left will be addressed rather than managed.

The upcoming NPT Review Conference in April-May presents an important opportunity to address proliferation debates. States should use it to reaffirm their non-proliferation commitments clearly and collectively, and to signal that the erosion of the arms control architecture is a shared concern. 

The World Today

Related work

Can the NPT review conference stop a new nuclear arms race?

Coordinated diplomatic pressure can raise the political costs of pursuing a weapons programme. The P5 should make it unambiguously clear that proliferation carries real consequences. They should point not to abstract principles, but to the lived reality of North Korea’s sustained isolation, which has caused great suffering to its people.

States considering nuclear development should also weigh the conventional alternative seriously. Long-range precision strike capabilities can replicate some of the deterrent effects of non-strategic nuclear weapons without the associated costs, escalation risks or international consequences. Strengthening conventional forces offers a credible path to enhanced security that upholds the non-proliferation regime.

The non-proliferation regime has survived difficult periods before. But it cannot survive indefinitely if the major powers continue to signal through their actions that nuclear weapons remain the only reliable guarantee of security. The window for reversing that signal is narrowing.