Well New Zealand is part of the Five Powers Defence Arrangement with the United Kingdom, Australia, Malaysia and Singapore the agreement was signed in 1971 whereby the five powers are to consult each other "immediately" in the event or threat of an armed attack on any of these five countries for the purpose of deciding what measures should be taken jointly or separately in response.
They hold regular military exercises, and this year (2021) the "Exercise Bersama Gold 21" is the 50th anniversary of the arrangement. But it is not an actual defence treaty and does not make them allies and there is no specific commitment to intervene militarily a threat arises.
New Zealand is a member of Five Eye's with is an intelligence gathering group Between the Australia, Canada, New Zealand, United States, and United Kingdom, however as stated above, intelligence gathering and sharing group nothing more, it is not a defence treaty and does not mean they are formal allies with New Zealand.
New Zealand was part of ANZUS until the mid 1980's and New Zealand's anti nuclear policies halted all that The US then suspended all treaty obligations with New Zealand. Downgrading New Zealand from 'ally', to 'friend'. ANZUS continued with Australia and the US.
- "The Collapse of New Zealand's Military Ties with the United States"
- AUKUS Defence Pact: New Zealand's exclusion reflects our 'friend, not ally' status with the US
- AUKUS: New Zealand labelled 'a joke' after nuclear-free stance blocks Australia's nuclear-powered submarines
- Distance between NZ and allies grows, as Australia brings nuclear submarines to the Pacific
However in 2010 the United States and New Zealand signed the Wellington Declaration in Wellington. The agreement signals closer relations between New Zealand and the United States, with an increase in the strategic partnership between the two nations. In doing so, the agreement stresses the continued pledge for the United States and New Zealand to work together, explicitly saying that: "The United States-New Zealand strategic partnership is to have two fundamental elements: a new focus on practical cooperation in the Pacific region; and enhanced political and subject-matter dialogue – including regular Foreign Ministers' meetings and political-military discussions." The agreement also stresses the continued need for New Zealand and the United States to work together on issues like nuclear proliferation, climate change and terrorism.
In 2012 the Washington Declaration between the United States and New Zealand, signed on 19 June 2012 at the Pentagon, established a framework for strengthening and building the basis for defense cooperation. The agreement was signed by New Zealand Defence Minister Jonathan Coleman and US Secretary of Defense Leon Panetta. While non-binding and not renewing ANZUS treaty obligations between the US and New Zealand, the Washington Declaration established the basis for increased defense cooperation between the two states.
All sounds good, but an important thing to note here, the two "Declarations" does not renew ANZUS it is non biding, and does not make New Zealand an ally of the US. It is a basic work around of the anti nuclear policy New Zealand has.
Australia is our only formal ally.
However in 1997 President Bill Clinton name New Zealand as "Major non-NATO ally" While the status does not automatically include a mutual defense pact with the United States, it still confers a variety of military and financial advantages that otherwise are not obtainable by non-NATO countries. The designation of New Zealand as an MNNA in 1997 reflected the warming of relations between the two. In June 2012 New Zealand signed a partnership arrangement with NATO further strengthening and consolidating relations.
One thing to note, NATO is not a country, and there is no formal obligations on either side to intervene. It is more, that New Zealand has helped out with several NATO lead operations, and because of this NZ can access a few things here and there via NATO. It is not a defence treaty as such.
Officially New Zealand now only has one formal official ally and that is Australia. The rest including UK, Canada, US, Japan, South Korea, are classed as friends, coalition partners. In a recent article written by the online Magazine DefSec did a interview with New Zealand's Secretary of Defence Andrew Bridgman. One of the questions asked about closer relations with Australia. Article can be read here.
Nicholas Dynon: In 2018 and again last year, the importance of Closer Defence Relations between Australia and New Zealand was emphasised. In a post-Covid 19 economic environment how important is it that we continue to work together to deliver capability in the most cost-effective way?
Andrew Bridgman: The short answer is that it’s extremely important. Australia is our only formal ally. By geography we logically have similar objectives, and by the numbers we are critical to each other. Even if you look at our respective defence forces, we are relatively small but we are material.
Note that he say's "Australia is our only formal ally" so when New Zealand's Secretary of Defence says New Zealand only has one formal ally it means New Zealand only has one formal ally. There is a difference between an official or formal ally and an unofficial or informal ally/friend or coalition partner etc.