NATO allies of the United States have continuously reiterated the alleged incompatibility between being a signatory to the Treaty on the Prohibition of Nuclear Weapons (TPNW) and their commitments under both the alliance and the Treaty on the Non-Proliferation of Nuclear Weapons (NPT). The common refrain is that the TPNW is little more than an anti-nuclear protest movement, that it undermines deterrence, and that it could even have serious repercussions for alliance cohesion in NATO. When challenged on these assumptions, European officials often repeat the NATO line that “as long as nuclear weapons exist, it will remain a nuclear alliance.”

This begs an important question: Is being a signatory to the TPNW at cross purposes with maintaining an alliance relationship with the US?

It does not follow that an anti-nuclear stance is by default ‘anti-alliance’. In the Pacific, New Zealand and the Philippines are both signatories to the TPNW and formal treaty allies of the US. Widening the aperture to include the South Pacific Nuclear Free Zone Treaty – also known as the Treaty of Rarotonga – brings in Australia (though not a TPNW member). Stepping back further, Rarotonga also applies to members of the Compact of Free Association with the US, specifically the Republic of the Marshall Islands.

Clearly, some states are able and willing to square the TPNW-alliance circle.

American allies supporting or even joining the TPNW would be an important step for nuclear non-proliferation and arms control at times of heightened nuclear risk.

(The TPNW differs from the NPT by establishing a categorical, legally binding prohibition on all nuclear weapon-related activities, whereas the NPT generally commits states to pursue disarmament but leaves the pace and form of that process open.)

In the context of the growing salience of nuclear deterrence in Europe and NATO – as well as discussions over indigenous nuclear weapons capabilities in some states – TPNW membership could become a non-proliferation instrument that complements the NPT and relieves some of the pressures currently facing extended deterrence.

Washington has justified its extended deterrent by presenting allies as proliferation risks, suggesting that if this protection is rolled back, those allies would develop weapons of their own. Viewing the TPNW as an additional guardrail against proliferation, similar to nuclear-weapons-free zones, could help alleviate this longstanding American concern.

In the words of former Australian Department of Foreign Affairs and Trade Assistant Secretary for Arms Control and Counter-Proliferation Peter Hooton, US allies signing the TPNW “would be providing further evidence of [their] determination not to acquire these weapons, and the United States would be spared any further need to pretend that it is holding a nuclear umbrella over [their] heads.”

Treating the TPNW as an alliance risk has been an impediment to arms control efforts. States allied with the US have argued that the TPNW is incompatible with alliance obligations, often to avoid confrontation with Washington over disarmament. Adopting a less confrontational, or even supportive, stance on the TPNW would not only create new momentum for nuclear disarmament, but also help US allies carve out a more independent path on arms control as the US becomes an increasingly irresponsible nuclear power and ally.

American attacks on Venezuela and Iran, the possibility of a return to nuclear testing, and an accelerating arms race – combined with growing doubts about the credibility and safety of extended deterrence – have all called into question the reliability of US leadership. For US allies, including in Europe, it is becoming increasingly dangerous to cling to Washington’s nuclear umbrella and hope for the best.

Pacific precedents

Such a pivot has already been seen in New Zealand. Since 1985, Wellington has pursued an anti-nuclear foreign policy, creating a long-running rift with Washington after the Reagan administration suspended its treaty obligations under the Australia, New Zealand, United States Security Treaty (ANZUS) when US navy ships were denied port visits. Rather than relenting, Wellington passed the New Zealand Nuclear Free Zone, Disarmament, and Arms Control Act of 1987, became an architect of the Treaty of Rarotonga, and is now a signatory and strong advocate of the TPNW.

Despite this enduring divide, the security relationship never fully ended. Though ANZUS obligations remain suspended, US-Kiwi security ties persist through the Five Eyes intelligence-sharing arrangement, the Australia, Canada, New Zealand, UK, US interoperability framework (ABCANZ), and the ABCANZ Armies programme for ground force icooperation. In this sense, an open break with the US is survivable for its allies, even if it has implications for the depth of the security relationship.

The case of the Philippines shows that even under conditions of geographic proximity to potential threats, alliance relations can coexist with an anti-nuclear stance and TPNW membership. Following the 1986 People Power Revolution, the new Filipino constitution explicitly rejected nuclear weaponry, and Manila went on to join the Treaty of Rarotonga and later the TPNW. The Philippines differs  in that US forces have not been blocked or directly challenged over their nuclear policy. Indeed, the rotational Task Force Philippines now operates in Luzon with Mid-Range Capability (MRC, also known as Typhon) systems – missiles that would be used to target China in the event of war. Still, despite deepening conventional military cooperation with the US, Manila maintains its constitutional provisions and treaty advocacy, even as it remains both geographically close to China and formally allied with Washington.

The lessons of New Zealand and the Philippines for other American allies are clear: security relations with the US can survive outside of extended deterrence relationships. This does mean that such relationships would differ from those based on nuclear sharing and extended deterrence, both of which are prohibited under the TPNW. This has been the strongest argument against the treaty among US allies, with opponents warning that joining it would increase the risk of nuclear coercion by Russia or China. The issue is often framed as a binary choice: sign the TPNW and risk coercion, or stay out and risk becoming part of a nuclear battlefield between the US and Russia and/or China.

As the Philippine case demonstrates, however, an anti-nuclear policy does not equate to complete disarmament. While conventional cooperation may not fully replace nuclear deterrence, it can provide a credible pathway for maintaining and enhancing security alongside anti-nuclear commitments. With the credibility of extended deterrence increasingly in doubt, and continued participation in nuclear sharing placing European allies on the front line of potential nuclear escalation, a meaningful commitment to disarmament alongside conventional capability development is a defensible strategic choice.

Where to begin?

TPNW membership and security relations with the US – even formal alliance membership – are not mutually exclusive. Treating them as such has impeded arms control, allowing states to avoid meaningful engagement with nuclear disarmament. The perceived incompatibility of TPNW membership and security relations with the US has also meant that the potentially positive role of the Treaty in reducing nuclear risks (such as creating additional guardrails to prevent nuclear possession), have been ignored by states allied with Washington.

As the US behaves with increasing unpredictability, it is becoming necessary for its allies to develop more independent foreign policy paths. Taking a leadership role on the TPNW could be part of that shift. This does not mean allies should immediately join the treaty, but rather that the assumption of incompatibility has unnecessarily constrained debate. Introducing greater nuance would improve understanding of both the opportunities and the genuine strategic constraints.

A first step would be to reopen parliamentary discussions on signing the TPNW, or at least becoming an observer. If a NATO ally were to sign, it would mark an important symbolic moment for arms control, particularly as the NPT regime continues to falter. Within NATO, some governments may be more open to this than others – for example, Spain, which has already clashed with Washington and other allies over Middle East policy. Unlike states that rely on US, UK, or French nuclear forces, Spain has remained outside nuclear-sharing agreements. A similar case could be made for Australia, a country so closely aligned with the US that it has at times been described as enthusiastically sub-imperial. With polling indicating as many as 68 percent of Australians support joining the TPNW, and with neighbouring states leading global disarmament efforts, the moment may be approaching.

The discussions would also need to address what TPNW implementation would mean in practice. For NATO allies, this would likely involve at least two concrete steps. First, withdrawal from the NATO Nuclear Planning Group and a clear opt-out from NATO’s nuclear planning process. Second, for nuclear-sharing countries, the removal of American B61 bombs and their associated US Air Force personnel.

Beyond these technical considerations, debates about the TPNW and US security relationships require far greater nuance. Reducing disarmament advocacy to caricatures of naivety ignores the lived realities of states such as New Zealand and the Philippines. As security relationships evolve and nuclear-armed states accelerate the arms race, what is needed are creative and credible foreign policy alternatives. Given the urgency of arms control and disarmament in the face of rising nuclear risks, reliance on an increasingly unstable security framework is becoming untenable.

The European Leadership Network itself as an institution holds no formal policy positions. The opinions articulated above represent the views of the authors rather than the European Leadership Network or its members. The ELN aims to encourage debates that will help develop Europe’s capacity to address the pressing foreign, defence, and security policy challenges of our time, to further its charitable purposes.

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