The Pacific Defence Pact is the wrong answer to the right question

Calls for a “Pacific Defence Pact” have gained traction in recent debates on Indo-Pacific security. Former Biden administration official Ely Ratner’s proposal for a formal, treaty-based framework reflects a growing concern: that existing arrangements among US allies remain too loose to deter a more assertive China.

Concurrently, there are some positive trends among US allies: minilateral initiatives are expanding, interoperability is improving and burden-sharing efforts are slowly increasing. These developments indicate the region is moving some way toward deeper integration, although not through formal treaties.

The central question is not whether deeper cooperation is needed but whether such a pact can work in practice. While the strategic rationale for enhanced cooperation is widely shared, the path to institutionalisation via treaty-based collective defence is fraught with challenges.

First, domestic constraints – especially in Japan – limit the extent of defence commitments. Japan’s constitutional framework and post-war security identity impose boundaries on Japan’s ability to enter collective defence obligations. From an Australian perspective, a formal pact would sharpen difficult trade-offs rather than resolve them – trade-offs such as making Australia a target for Chinese retribution, and raising US expectations regarding Australian defence spending.

Second, the regional context – particularly in Southeast Asia – complicates the acceptance of highly institutionalised, bloc-oriented security arrangements. Many Southeast Asian countries prioritise strategic autonomy and are wary of appearing too closely aligned with any one bloc, especially in ways that could antagonise China or undermine their own diplomatic flexibility. The diversity of regional perspectives means that a one-size-fits-all, formal alliance is unlikely to gain broad acceptance.

Third, questions persist about the credibility of formal commitments in an era of shifting US strategic consistency and political direction. Allies and partners in the region are acutely aware that US domestic politics can affect the reliability of American security guarantees. This uncertainty undermines the perceived value of formal treaties and may discourage countries from seeking deeper institutionalised commitments.

A treaty-based approach risks exacerbating resistance among regional actors, undermining the legitimacy of such arrangements and failing to deliver measurable improvements in deterrence. Instead of resolving strategic ambiguity, a treaty-based framework might provoke tensions, diminish regional buy-in, and create a false sense of security.

The Indo-Pacific’s political, cultural and strategic diversity means flexibility and adaptability are essential. Security cooperation must accommodate varying levels of commitment, operational capacity, and willingness among participants. Imposing a uniform structure carries the risk of alienating key partners and reducing the effectiveness of regional security efforts.

What matters is how states work together in practice. In this way, it is helpful to conceptualise Indo-Pacific security cooperation as a layered process rather than a linear progression from informality to formality.

At the core of Indo-Pacific collective defence is a highly aligned trilateral framework between the United States, Japan and Australia. This core group provides a strong foundation for deeper cooperation, building on shared interests, high levels of interoperability and longstanding defence relationships.

Beyond this, functional, modular and mission-oriented mechanisms – such as the Enforcement Coordination Cell (ECC) – offer a flexible, scalable model for expanding cooperation. These mechanisms focus on specific tasks or missions, such as sanctions enforcement or maritime surveillance, and can adapt to circumstances without requiring commitment to a single, rigid structure. Mechanisms of this type are more compatible with Southeast Asian perspectives – avoiding the binary choice between alignment and non-alignment – and create space for engagement without forcing countries into formal blocs.

The layered model enables “minilateralism”, cooperation among small groups of like-minded countries tailored to particular issues or contingencies. The ECC, Bilateral Intelligence Analysis Cell in Yokota Air Base and US-Philippine Combined Coordination Centre near Manila exemplify how partners can integrate intelligence-sharing and operational analysis without requiring a comprehensive treaty framework. This approach recognises that not all regional actors share the same threat perceptions or strategic priorities. It delivers something formal structures often struggle to provide: operational integration.

The future of Indo-Pacific security cooperation will depend less on institutional form than on operational credibility and regional legitimacy. Recent crisis simulations involving the United States, Japan, and Australia suggest that even highly aligned partners with strong institutional understanding do not always respond in a coordinated or predictable way under pressure, with differences in risk tolerance, economic priorities, and crisis management approaches. While the desire for stronger collective defence is understandable, replicating alliance models from other regions is unlikely to succeed in the Indo-Pacific context.

Indo-Pacific security cooperation depends less on what states promise on paper than on what they can deliver together in practice. The layered approach – anchored by a strong core group and augmented by flexible, mission-oriented arrangements – offers a pragmatic pathway in a region marked by complexity and uncertainty. This approach is not a retreat from ambition, nor does it preclude the possibility of greater formalisation in the future. But for now, security cooperation in the Indo-Pacific will be measured not by the existence of treaties, but by the ability of regional states to act together when it matters.