A comprehensive defence treaty between Japan and Australia is overdue. The 50th anniversary of the two countries’ Basic Treaty of Friendship and Cooperation, to be marked this year, should provide the occasion for signing an expanded agreement – one that strengthens defence cooperation but not going as far as obliging either country to go to war in defence of the other.
The need for closer Japan–Australia defence cooperation is growing, yet existing agreements remain limited in scope. Expanding cooperation issue by issue would be slow and cumbersome, as seen in the case of the Australia–Japan Reciprocal Access Agreement, which was finalised only after seven years of negotiation.
A treaty that facilitates deeper and broader cooperation is becoming increasingly necessary as the importance of the relationship grows amid a deteriorating strategic landscape. Such a treaty should recognise each country’s importance to the other’s defence, commit them to consult and respond to contingencies affecting their sovereignty and regional security interests, and ensure that appropriate measures and preparations are in place. This essentially means an upgrade of the 2022 Japan–Australia Joint Declaration on Security Cooperation to a treaty that would provide legal basis for further cooperation.
Historically, Japan–Australia defence cooperation has lacked a formal legal foundation because many security experts have assumed that a treaty would entail mutual defence obligations similar to those found in formal alliances. Furthermore, no broad treaty has been feasible, for three main reasons.
First, there was formerly little strategic need. Japan and Australia were each allied to the United States, which would have led any combined defence operation in the Indo-Pacific. If the United States had chosen not to intervene militarily against Chinese action, Japan and Australia alone couldn’t realistically have done so.
Second, Japan’s constitutional constraints would have made such a Japan–Australian alliance unbalanced. Under the current interpretation of the constitution, Japan can exercise collective self-defence only when an attack on a partner threatens its own survival. Australia’s value in defending Japan wasn’t likely to be considered decisive, so an attack on Australia wouldn’t threaten Japan’s survival. Japan therefore couldn’t act to defend Australia, even though Australia could act to defend Japan.
Third, the modest level of cooperation required in the former, less dangerous strategic environment could largely be achieved through frameworks such as the 2022 Joint Declaration on Security Cooperation and the Acquisition and Cross-Servicing Agreement.
Today, however, the strategic environment has deteriorated more rapidly than expected, and the importance of bilateral cooperation is increasing, creating a growing need for a broader legal framework even if it stops short of creating a formal alliance.
Increasingly uncertain US commitment to defending partners in the region and its weaker coordination with allies globally are raising new risks for Japan and Australia. Although the regional balance of power still requires a strong US presence – and it remains unrealistic for Japan and Australia alone to counter China – there is increasing need for a framework that enables them to complement each other’s defence capabilities. Stronger and more direct bilateral ties will therefore be essential.
Japan increasingly views Australia as its most important security partner in the region. A senior Japanese government official told me privately last month, ‘Japan’s defence has thus far been sustained 95 percent by its own efforts and the Japan–US alliance. Going forward, the percentage of the alliance may decrease, while partners such as Australia are likely to assume a much greater role in Japan’s defense.’ Although Japan cannot commit in advance to defending Australia, treaty recognition of Australia’s indispensable role in Japan’s defence would make Japan much more likely to judge that an attack on Australia would threaten its own survival.
As bilateral cooperation deepens, it may soon exceed what existing frameworks can accommodate. For example, Japan needs large missile depots beyond China’s densest strike-missile coverage. They could be in Australia, but only under suitable treaty terms. Japan could also use Australia’s dry environment for storage of mothballed equipment, such as tanks. Yet no legal framework currently supports such arrangements.
The absence of such a framework also prevents bilateral operational planning. As the two governments expand cooperation in areas such as integrated air and missile defence and the protection of sea lines of communication, Japan lacks a legal basis to plan operations jointly without US involvement. Even as Australia’s importance to Japan’s defence grows—and an attack on Australia may be seen as threatening Japan’s survival—the two countries still lack the legal basis to prepare joint operational plans.
A treaty recognising Australia’s strategic importance to Japan and providing a broad legal foundation for cooperation would help address these challenges.
The 2022 Japan–Australia Joint Declaration on Security Cooperation should therefore be upgraded to a treaty. Importantly, such a treaty would not require mutual defence obligations. Australia has already demonstrated that defence cooperation treaties without such commitments are possible, as seen in its treaty with Indonesia.
The 50th anniversary of the signing of the bilateral treaty, coming up in June, would be a politically suitable time to take this step.
Japan and Australia should seize this opportunity to establish a durable legal foundation for defence cooperation – one that could shape the next 50 years of their strategic partnership.