In June, Coast Guard ships hailing from the United States, the Philippines, and Japan undertook joint operations near Japan’s Kagoshima prefecture, on the cusp of the East China Sea. At a time when China is wielding its own Coast Guard to bully neighbors and craft a new regional order defined by deference to Beijing, the multinational fleet sailing through Kagoshima Bay sent a powerful signal of resolve that would have been difficult to imagine just a few years earlier.
If you ask policymakers in Washington or Tokyo about trilateral cooperation in Asia, most will talk about the importance of the hard-won partnership between the United States, Japan, and South Korea. But out of the limelight, the “other trilat” is becoming a uniquely formidable partnership. Launched at a 2023 meeting of the three countries’ national security advisors, the U.S.-Philippines-Japan trilateral partnership seized on Japan’s growing sense of responsibility for regional security, unprecedented momentum in the U.S.-Philippines alliance, and a common belief that the region’s most pressing challenges could be solved only through collaboration among like-minded countries.
In June, Coast Guard ships hailing from the United States, the Philippines, and Japan undertook joint operations near Japan’s Kagoshima prefecture, on the cusp of the East China Sea. At a time when China is wielding its own Coast Guard to bully neighbors and craft a new regional order defined by deference to Beijing, the multinational fleet sailing through Kagoshima Bay sent a powerful signal of resolve that would have been difficult to imagine just a few years earlier.
If you ask policymakers in Washington or Tokyo about trilateral cooperation in Asia, most will talk about the importance of the hard-won partnership between the United States, Japan, and South Korea. But out of the limelight, the “other trilat” is becoming a uniquely formidable partnership. Launched at a 2023 meeting of the three countries’ national security advisors, the U.S.-Philippines-Japan trilateral partnership seized on Japan’s growing sense of responsibility for regional security, unprecedented momentum in the U.S.-Philippines alliance, and a common belief that the region’s most pressing challenges could be solved only through collaboration among like-minded countries.
This partnership now offers tremendous potential for deterring Chinese aggression in the Western Pacific, bolstering the region’s rules-based order, and enhancing the three countries’ security and prosperity. China itself has endorsed the group’s significance, with a Foreign Ministry spokesperson responding angrily to a 2024 meeting of the three countries’ leaders: “They should not introduce bloc confrontation into this region, still less engage in trilateral cooperation at the expense of other countries’ interests.”
The trilateral partnership among the United States, the Philippines, and Japan now has the potential to become a central platform for countering China’s destabilizing maritime and economic coercion. It is underwritten by strong treaty alliances between the United States and the Philippines as well as the United States and Japan. While the Philippines and Japan lack a formal bilateral alliance, they have established robust security ties. The Philippines is the largest recipient of Japan’s Official Security Assistance, and in September, a Philippines-Japan Reciprocal Access Agreement (RAA) came into force; this enables each country’s troops to deploy on the other’s soil on a rotational basis. But the three countries must institutionalize their grouping without delay—before political headwinds waylay a historic opportunity.
The Indo-Pacific has no shortage of minilateral partnerships. The “original” trilateral is better suited for tackling the nuclear threat posed by North Korea. The Quad (comprising Australia, India, Japan, and the United States) is more appropriate for delivering global public goods and countering China’s malign activities beyond the Western Pacific.
But these pivotal groupings have limitations. While India agrees with the other Quad members that China represents a security threat, it prefers a multialigned solution including a close partnership with Russia, which is itself a close partner of China. The Quad’s global agenda is strengthened by its far-flung geography, but for tackling the most pressing regional challenges in China’s maritime periphery, this can be a disadvantage. Within the U.S.-South Korea-Japan partnership, Seoul has traditionally placed less priority on addressing threats from China, which it views as a key economic partner, if an untrustworthy one.
By contrast, the “other trilat” believes that China represents an urgent national security challenge, and all three countries have prioritized action to strengthen their own defense capabilities, counter China’s maritime coercion, limit economic vulnerabilities that China could exploit, and harden their communication networks against Chinese infiltration. They recognize that peace and stability across the Taiwan Strait are essential for their own security and prosperity, and they have each sought to partner with Taiwan and oppose Beijing’s belligerent erosion of the cross-strait status quo.
It will be important for the U.S.-Philippines-Japan partnership to strive for complementarity with the activities of like-minded groupings. Yet on key issues, these three countries may ultimately be able to move further and faster.
Critically, the geographic scope of the U.S.-Philippines-Japan partnership allows for a comprehensive approach to deterrence across the East China Sea, South China Sea, and the waters around Taiwan. China’s maritime forces have deployed similar coercive gray-zone tactics against Japanese and Philippine ships in the East China Sea and South China Sea, respectively, and also against Taiwan, which sits merely 61 miles from the northernmost Philippine island and 70 miles from Japan. The United States, meanwhile, is the only country aside from China that maintains a persistent operational presence throughout all of these areas.
China, for its part, views its maritime periphery as a single strategic theater. Its appetite for risk in any part of the East China Sea, South China Sea, or the waters around Taiwan is shaped by the degree to which it meets resistance across the rest of that geography. Together, the United States, the Philippines, and Japan can establish a common operating picture as well as a common deterrence strategy across this area. This would allow the three countries to more effectively counter Chinese aggression and advance their own security, as well as cross-strait peace and stability, while buttressing the regional rules-based order. To avoid Beijing’s ire, the other Southeast Asian countries that have suffered China’s bullying in the South China Sea are unlikely to publicly welcome such endeavors. But they will surely benefit from an operational environment that is less permissive for Chinese maritime coercion.
The United States, the Philippines, and Japan have complementary strengths and capabilities that enable high-impact collaboration, particularly with respect to maritime affairs, economic resilience, and communication networks. Building on the existing Coast Guard exercises and a trilateral maritime dialogue that first met in 2024, they are well positioned to expand maritime cooperation further. The U.S. military has established nine sites at Philippine bases, mostly in coastal areas, pursuant to the two countries’ Enhanced Defense Cooperation Agreement. At these sites, the U.S. military can build infrastructure, deploy troops on a rotational basis, and preposition materiel.
With the Philippines-Japan RAA now in force, Japan could deploy its own service members to these sites, facilitating more advanced trilateral maritime exercises, as well as humanitarian assistance and disaster relief activities during typhoon season. Likewise, members of the Philippine Coast Guard and Navy could deploy to U.S. bases in Japan, sending an unmistakable signal of allied solidarity and readiness. The three countries could facilitate real-time maritime information-sharing by developing a trilateral General Security of Military Information Agreement (GSOMIA), building on the 2024 U.S.-Philippines GSOMIA and the Philippines-Japan GSOMIA now under negotiation.
The three countries have also worked to strengthen their economic resilience, promoting inclusive growth while mitigating vulnerabilities that could be weaponized by China to seek concessions in the South or East China Sea or otherwise punish resistance to China’s will. The Luzon Economic Corridor is the partnership’s flagship economic initiative; it is intended to facilitate north-south connectivity and infrastructure investment across the Philippines’s largest island, including a freight rail line that will ease the logistics of transporting cargo between key ports and cities. There are many opportunities for enhancing port and energy infrastructure along the corridor and for pursuing trilateral cooperation in shipbuilding, tailored to Philippine strengths in maintenance and repair operations.
The utility of enhanced connectivity and ship maintenance in a crisis is clear, but coming together to bolster Philippine economic security delivers an immediate strategic advantage as well. It lessens the Philippines’s vulnerability to coercion by ensuring that critical infrastructure is delivered by allies rather than China—which in turn provides the Philippines with more space to contribute to allied deterrence.
Furthermore, the three countries have come together to facilitate Open RAN (known as “O-RAN”) adoption in Philippine 5G networks, which creates market opportunities for trusted vendors and complicates China’s efforts to infiltrate Philippine communication infrastructure. The O-RAN Interoperability Lab, built and operated in Manila with support from the U.S. and Japanese governments, provides a venue for Philippine professionals to access O-RAN training and testing, in partnership with U.S. and Japanese technology companies. Moving ahead, the countries’ development finance agencies should work to mobilize private capital in support of the Philippines’s 5G rollout and other communications infrastructure needs, scaling up the lab’s initial impact.
Notwithstanding all this progress and potential, political roadblocks lie ahead. In the Philippines, President Ferdinand Marcos Jr. has bet his legacy on the United States and its alliance network delivering for the Philippines and has strongly supported the trilateral partnership. But by 2027, Marcos will increasingly be considered a lame duck ahead of the 2028 presidential election, which could easily deliver a government more skeptical of the United States and accommodating toward China. The United States and Japan have sky-high favorability ratings among the Philippine public, and the next president will find it difficult to cancel existing cooperative mechanisms, but there may be limited appetite for new ones.
For its part, the Trump administration has embraced the U.S. alliances with Manila and Tokyo, providing large development assistance grants to the Philippines and prioritizing an official visit to Japan immediately after Prime Minister Sanae Takaichi’s election. U.S. Secretary of State Marco Rubio issued an enthusiastic statement following a trilateral meeting with his Philippine and Japanese counterparts in July. Still, U.S. President Donald Trump’s harsh tariffs against both allies (alongside most other countries) are straining these relationships, and for that reason as well, it may become more difficult over time to routinize new forms of cooperation.
Ahead of challenging political winds in the years to come, the United States, the Philippines, and Japan now have an opportunity to institutionalize their partnership. Since 2023, their national security advisors, foreign ministers, and commerce ministers have met trilaterally, and in 2024, the three leaders met at the White House. But these engagements were largely ad hoc and opportunistic.
Each government can make a strong argument to its political stakeholders regarding the value of trilateral cooperation. Marcos can point to its wide-ranging benefits; not only does the partnership help the Philippines uphold its sovereign rights in the South China Sea, but it also delivers much-needed jobs, upskilling, and infrastructure. Takaichi’s campaign platform emphasized plans to strengthen the U.S.-Japan alliance and expand Japan’s regional engagement. The trilateral can provide her with quick wins, illustrating her ability to deliver on key promises. Trump can point to his success in pressing allies to assume greater responsibility for their own security.
The three countries should now establish an annual program of meetings at the leader and ministerial levels, which will ensure high-level focus and momentum over the longer term. Takaichi has indicated that she will soon revise the government’s national security and defense strategies; the trilateral partnership should also be memorialized in these documents. The Trump administration could also highlight the partnership in its forthcoming National Security Strategy.
Looking to the future, it is clear that institutionalization and expansion of the U.S.-Philippines-Japan trilateral partnership will empower the three countries to undertake a compelling, affirmative agenda that counters Chinese aggression, advances resilience to Chinese coercion, and bolsters the postwar regional order. There is no time to waste.
