Australia and Papua New Guinea on Monday signed a major mutual defense treaty seen as mainly intended to offset China’s expanding military clout in the South Pacific and prevent Beijing from projecting power through Australia’s northern approach.

The deal, which will elevate the long-standing relationship to a formal alliance, was signed by Australian Prime Minister Anthony Albanese and his Papua New Guinea counterpart, James Marape, in Canberra after the Papua New Guinea Cabinet formally approved the landmark deal last week.

Known as the Pukpuk Treaty, in reference to the Papua New Guinean pidgin word for "crocodile," the pact was initially set to be signed on Sept. 17 alongside celebrations for Papua New Guinea’s 50th anniversary of independence from Australia. However, the two countries issued only a joint communique at that time, as the Papua New Guinea Cabinet lacked the required quorum.

Once ratified by each country's parliament, the Pukpuk Treaty will mark Australia’s first new alliance in more than 70 years, and only the third in its history alongside those with New Zealand and the United States.

The deal, which commits the neighboring nations to come to each other’s aid if attacked, comes at a time of growing geostrategic competition in the Pacific between China and the U.S. and its allies.

Besides the mutual defense obligation, the pact outlines the expansion and modernization of the two countries’ defense relationship.

This includes establishing a recruitment pathway for Papua New Guinea citizens into the Australian military. More precisely, it includes provisions for up to 10,000 Papua New Guineans to serve with the Australian military while Papua New Guinea builds up its own 7,000 strong defense force.

While this would help Australia overcome recruitment issues, experts such as Sebastian Maslow, an associate professor at the University of Tokyo, warn that this provision also risks Papua New Guinea nationals disproportionately joining the higher-paid Australian military, potentially weakening Papua New Guinea’s own military capabilities.

That said, the pact also outlines additional resources for the modernization of the Papua New Guinea Defence Forces across all domains, including to patrol and protect the country’s vast maritime boundaries and resources.

“The treaty seems to promise much needed investment in the PNGDF, which suffers from a dilapidated defense estate and low operational experience,” said Mike Hughes, director of defense strategy at the Australian Strategic Policy Institute think tank.

It also envisions that the countries’ armed forces enhance capability, interoperability and integration, with the Australian Broadcasting Corp. reporting that the move would also give the Australian military unimpeded access to a number of locations within Papua New Guinea.

“Canberra has already been investing in strategic assets in PNG such as the Lombrum Naval Base, and these efforts are likely to be elevated under the new pact,” Maslow said, referring to Papua New Guinea by its acronym.

Speaking to reporters last week, Marape said the deal envisages investments “in both hardware and software for defense so that we can effectively police our borders and safeguard our nation.” He also emphasized that Papua New Guinea sovereignty would remain intact as the pact includes provisions to respect each other’s relations with third parties.

The Papua New Guinea leader has repeatedly stated that the treaty was his idea, arguing that the country’s defense capabilities would not be sufficient in the event of an invasion — making a security alliance with Australia necessary.

But while Australia may perceive China as its biggest security threat, Papua New Guinea faces no imminent threat of an attack or invasion as most of its security issues involve internal and localized conflicts.

The strategic significance of the treaty therefore lies in Papua New Guinea’s geographic location.

Sitting at the foot of the “second island chain” with Asia to the north and the South Pacific to the east, the island nation, which shares a land border with Indonesia, is a key point for both the U.S. and Australia.

This explains why the country has been a focal point of efforts to integrate it into the Western-led regional security architecture, particularly after China’s 2022 security pact with the Solomon Islands. The results have been visible, with Papua New Guinea co-hosting the large-scale Talisman Sabre military exercises earlier this year for the first time.

“For Australia, PNG has occupied strategic thought and invoked concerns about being a launchpad for invasion of Australia since the 1800s,” given its geographic proximity, Hughes said, pointing out that Papua New Guinea is Australia’s closest neighbor, lying just 2 kilometers at its closest from Australia's northern tip.

Any military presence there by a rival power would therefore impact Australia’s ability to secure critical sea lines of communication running through this region — routes that would be vital in any regional security crisis.

Oliver Nobetau, project director of the Australia-Papua New Guinea Network at the Lowy Institute, said that, with the treaty expected to also contain an element giving Australia access to strategic locations, “this can be seen as an important step towards keeping China at bay.”

Papua New Guinea’s geostrategic importance has also long been recognized by other countries, including Japan and the U.S.

In May 2023, Washington signed two landmark security pacts with Port Moresby. One of them — the Defense Cooperation Agreement — grants U.S. forces “unimpeded access” to six sites in the Pacific island country, including a key naval base.

The other, aimed at improving maritime domain awareness and countering threats such as illegal fishing and trafficking, turned Papua New Guinea into another participant in the U.S. Shiprider program.

Maslow noted that the Australia-Papua New Guinea pact’s deterrence value — as well as its contribution to U.S.-led efforts to contain China’s regional military presence — might hinge on its precise terms, including whether the text resembles NATO’s Article 5 on collective defense, or Article 4 on consultations.

Deterrence will also depend on the scale of investment Australia and its allies commit to when modernizing the Papua New Guinea military and deploying key assets to the area.

For Papua New Guinea, the pact represents a delicate balancing act, between preserving sovereignty and avoiding alienating China — now a major investor — while at the same time deepening security ties with Australia, Maslow said.

The deal also marks a diplomatic victory for Australia after suffering a setback with Vanuatu, whose Cabinet paused the signing of a landmark security and development agreement with Canberra last month amid concerns it could limit the Pacific island nation’s ability to receive infrastructure funding from other countries, particularly China.