A literal reading of the treaty suggests that ANZUS is a triangle. According to the all-important fourth article ^[1], each one of the three parties ‘recognizes that an armed attack in the Pacific Area on any of the Parties would be dangerous to its own peace and safety and declares that it would act to meet the common danger in accordance with its constitutional processes’.

But the spirit of the law isn’t the same as the letter. ANZUS established the strongest party as the regional security provider for the other two, whose obligations primarily are to support Washington as the dominant Asia–Pacific power. This meant that ANZUS wasn’t so much a triangle as a chevron with the US sitting at the apex. (Confused? Next time you spot a Citroën, look for the double chevron.)

When the US suspended its alliance obligations to New Zealand during the mid-1980s nuclear policy crisis, the chevron gave way to a single straight line. For Australian audiences, ANZUS became the bilateral alliance connection between Canberra and Washington, reflected in the regular AUSMIN consultations. On the other side of the ditch, ANZUS became the alliance that New Zealand used to have with the US. Politicians across New Zealand’s electoral spectrum found there was no domestic political gain in restoring those alliance links. Returning to New Zealand after signing the 2012 Washington Declaration with Leon Panetta, Defence Minister Jonathan Coleman insisted ^[2] that Wellington’s strengthening security partnership with the US wasn’t ‘ANZUS in drag’.

How then to talk about the alliance connection between Australia and New Zealand, the third and consistently quieter leg of ANZUS? Governments in Wellington have adopted the formula of referring to Australia as New Zealand’s only formal ally. Declarations of fealty to that relationship regularly pepper New Zealand defence policy statements. The most recent defence white paper, issued in 2016, stipulates that ‘New Zealand has no better friend and no closer ally … While a direct armed attack on Australia is unlikely in the foreseeable future, should it be subject to such an attack, New Zealand would respond immediately.’ As for operations further afield, the 2018 strategic defence policy statement observes that the New Zealand Defence Force (NZDF) ‘must be able to operate effectively with New Zealand’s key security partners and ally Australia’.

But neither document mentions ANZUS. Both place the trans-Tasman military connection in the context of Closer Defence Relations (CDR), which was an initiative established in 1991 to mirror Closer Economic Relations. Yet CDR is not itself an alliance, and the 1944 Canberra Pact (in which New Zealand and Australia outlined their postwar plans for cooperation in the South Pacific) lacks the military obligations set out in the ANZUS Treaty less than a decade later. And, while the Anzac connection is a great talking point when prime ministers meet, the idea of an unbroken train of trans-Tasman military cooperation since the Gallipoli landings is an untenable myth.

The military alliance between New Zealand and Australia has an obvious source, which is ANZUS. There’s a small hint of this reality in the 2018 CDR Joint Statement ^[3]: ‘The formal expression of our alliance and security partnership is found in the 1944 Canberra Pact, ANZUS Treaty and through Australia – New Zealand Closer Defence Relations instigated in 1991.’ But that framing is oblique enough to allow New Zealand to carry on its merry way. And yet that’s not how Canberra always likes to portray things. ‘We are close partners and ANZUS allies,’ says Australia’s (still current) 2016 defence white paper. In a May 2021 press conference with Jacinda Ardern in Queenstown, Scott Morrison weighed in ^[4] on similar terms. ‘ANZUS arrangements were clear,’ he said, when asked if Canberra would expect Wellington’s support should Australia end up in an armed conflict with China in the Taiwan Strait or South China Sea.

You say ANZUS, I say alliance, let’s not call the whole thing off is the line New Zealand sings to Australia. Yet, spoken about or not, ANZUS alliance obligations run across both sides of the Tasman Sea. Wellington would expect itself to respond to a direct attack on Australia. But the scenario Morrison was asked about might see New Zealand do an Alexander Downer ^[5] and interpret its ANZUS obligations imaginatively. The recent saga over New Zealand’s approach to Five Eyes messaging to China on human rights reveals that Wellington wants some wiggle room. Sometimes Wellington will come to the party, other times it won’t, and all we’re talking about here are joint statements by foreign ministers. The commitment of New Zealand forces to a conflict that Australia is participating in raises the costs of commitment far higher.

There’s a real limit to how far Wellington will want its alliance commitments to Australia couched in Indo-Pacific terms, even though there are some NZDF capabilities (especially the forthcoming P-8 Poseidon aircraft) that could be useful to a coalition effort. But in between the defence of Australia and maritime combat in East Asia is a part of the regional real estate that could be the real test of New Zealand’s alliance commitments.

The South Pacific is where Australia and New Zealand are most intensely united in seeking a favourable equilibrium of power. Australian forces are very unlikely to engage the People’s Liberation Army on their own in a Taiwan Strait contingency. But in the South Pacific, a direct Australia–China clash, with or without the help of America (which delegates a great deal to Canberra’s leadership), could be more conceivable.

Should it get into warlike difficulty with China in a tussle for influence over Papua New Guinea’s future, for example, Australia wouldn’t just expect New Zealand’s help. Canberra would be likely to demand it. And should New Zealand demur, a crisis would emerge in trans-Tasman alliance relations that could make the mid-1980s look like a cakewalk.

Three and half decades on from the suspension of America’s alliance relations with New Zealand, the big ANZUS moment for Wellington could have more to do with Beijing and Canberra than with Beijing and Washington. This gives New Zealand extra reasons to be concerned about the deteriorating China–Australia relationship.

This post is an excerpt from ANZUS at 70: the past, present and future of the alliance ^[6], published by ASPI with support from the American Chamber of Commerce in Australia and edited by Patrick Walters.