ASEAN, explained.

Technicians at the Kartini Nuclear Reactor in Indonesia with a radioactive warning sign in the foreground (DEVI RAHMAN/AFP via Getty Images)

Research facilities like the Kartini Nuclear Reactor in Indonesia are found in Southeast Asia but the regional treaty has helped ensure countries remain free of nuclear weapons (DEVI RAHMAN/AFP via Getty Images)

Southeast Asia’s nuclear weapons-free zone needs reinforcement

As nuclear risk returns globally, Southeast Asia's weapons-free status looks less secure and more worth defending.

Brendan Taylor

4 March 20264 min read

Nuclear weapons are dominating headlines. US strikes against Iran. Allegations of Chinese nuclear testing. The expiry of New START, which until February was the last strategic arms control treaty between the world’s two largest nuclear powers.

As nuclear danger rises, it is important not to miss the quieter restraints that still hold. One sits in Southeast Asia. The Southeast Asia Nuclear Weapon-Free Zone (SEANWFZ), created by the 1995 Bangkok Treaty and in force since March 1997, has endured for almost three decades. In Australia, it draws little serious attention.

Australia is not a party to the treaty but has benefitted from it and has a clear interest in Southeast Asia remaining free of nuclear weapons. The treaty will not determine what China and North Korea do with their arsenals, or whether America continues to run the risks required to shelter allies under its nuclear umbrella.

But it would be a mistake to assume that Southeast Asia won’t ever go nuclear. In strategy, what becomes thinkable often matters as much as what is immediately feasible.

Seen in this way, what could cause Southeast Asia’s non-nuclear status to fray and what can Canberra do to help sustain it?

Pressure on SEANWFZ could come from three directions.

First, as great power rivalry intensifies, its nuclear dimension will be harder to keep out of Southeast Asia’s security environment. SEANWFZ was meant to help keep the region outside nuclear politics, including by drawing the nuclear-armed states into a protocol of legally binding assurances. Yet none of the established nuclear-armed powers have signed it, despite longstanding ASEAN efforts and Beijing’s professions of readiness to do so. The zone therefore binds its members more than the powers whose forces operate around them.

Australia can help put nuclear restraint back on the regional agenda in a way that is neither sanctimonious nor procedural.

That matters because pressure on SEANWFZ is more likely to come through routine operations than any dramatic breach. Nuclear-capable forces - especially submarines and other long-range strike platforms - can operate in and around Southeast Asia in ways that cannot readily be distinguished from purely conventional activity. Article 7 of the treaty leaves port visits and transit to national discretion “on being notified”. But notification is not verification. In time, the treaty may still exist largely in name while nuclear-capable operations become a new normal in regional competition.

The second pressure is transmission from Northeast Asia. SEANWFZ was born partly out of anxiety about North Korea’s nuclear program and fears that it could pull others, especially Japan, into the game. The more plausible trigger today is South Korea, where support for an indigenous nuclear capability has been polling well above 70%. If Seoul ever went nuclear, Tokyo would come under intense pressure to follow. Prime Minister Sanae Takaichi has wavered when pressed on Japan’s three non-nuclear principles, echoing her mentor Shinzo Abe’s efforts to make nuclear options less taboo. In that climate, SEANWFZ matters more, but it is also under greater stress, because nuclear weapons feel less remote and Southeast Asian hedging starts to look prudent.

The third, quieter pressure is neglect. Treaties do not sustain themselves. They require political care, periodic renewal and sustained diplomacy. A nuclear weapon-free zone cannot be treated as a legacy artefact, taken off the shelf for anniversaries and otherwise ignored. SEANWFZ will lose credibility if it comes to be treated as optional by outsiders and as ritual by insiders. Once credibility weakens, the treaty remains, but it no longer influences what governments assume, plan for, and tolerate.

Australia’s influence is limited, but not irrelevant. Canberra can help sustain the conditions in which restraint remains politically viable, especially by supporting partners who want to keep nuclear weapons out of Southeast Asia.

A starting point exists in ASEAN’s own architecture. Australia, the Philippines and New Zealand currently co-chair the ASEAN Regional Forum’s (ARF) non-proliferation and disarmament stream, while Australia and the Philippines have used the ARF to run nuclear risk reduction workshops. That effort is useful and should continue. But the ARF is not built for urgency, and nuclear risk is returning faster than its processes can move.

What is missing is a political intervention substantial enough to match the problem. Writing recently in Australian Foreign Affairs, former foreign minister Gareth Evans argued that Prime Minister Anthony Albanese should give a major speech setting out the nuclear arms control story - from elimination efforts, to non-proliferation, to risk reduction - and what Australia can contribute to each. But Evans didn’t specify where such a speech should be delivered. If Southeast Asia is where nuclear pressures are building and where restraint still has real political meaning, then a major Southeast Asian capital, or the margins of an ASEAN leaders’ meeting, is the right stage.

With Manila as ASEAN chair in 2026, Australia has a close partner to make that moment count: to put nuclear restraint back on the regional agenda in a way that is neither sanctimonious nor procedural. Such a move would also reinforce Canberra’s commitment to nuclear non-proliferation at a time when AUKUS has raised questions in parts of the region. In this new atomic age, Southeast Asia’s non-nuclear status will not be preserved by treaties alone. It will depend on repeated choices by Southeast Asian governments to keep nuclear weapons off the table, and on partners willing to invest real diplomatic capital in that restraint.