Southeast Asia’s mainland–maritime defence partnership divide

China’s efforts to replace the United States’ security role and influence in Southeast Asia are gaining traction, with Beijing becoming a key defence partner to several mainland countries, a new Lowy Institute Analysis reveals.

The paper by Rahman Yaacob, Susannah Patton, and Jack Sato, entitled Southeast Asia’s evolving defence partnerships, analyses Southeast Asia’s defence agreements, dialogues and combined military exercises with ten countries: Australia, Canada, China, France, India, Japan, Russia, South Korea, the United Kingdom, and the United States.

The United States remains the top overall defence partner for Southeast Asia, while China ranks eighth.

But the Analysis reveals a clear divergence between maritime Southeast Asia (Brunei, Indonesia, Malaysia, the Philippines, Singapore, and Timor-Leste), where the United States is dominant, and mainland Southeast Asia (Cambodia, Laos, Myanmar, Thailand, and Vietnam), where China is increasingly influential in most countries.

“China has invested substantial effort in establishing greater defence cooperation with Southeast Asian countries, and it likely intends to emulate and compete with the United States in this domain,” said co-author and Lowy Institute Deputy Research Director Susannah Patton.

“Beijing has made steady progress, particularly in mainland Southeast Asia. Further inroads, especially if nascent defence cooperation with Indonesia and Malaysia were to become more substantial, would add to China’s narrative and provide it with new pathways to pursue its interests.”

At the same time, the report shows middle powers, such as Australia, Japan and South Korea, have become more important, as Southeast Asian countries reshape their defence engagement strategies to safeguard their autonomy and boost regional stability amid intensifying strategic competition.

But the authors warn that if existing partners continue to overlook the region’s smaller mainland countries, such as Laos and Cambodia, there is a risk of entrenching the existing mainland–maritime divide.

“If current trends persist, Southeast Asia risks dividing into two camps: maritime countries with deep defence ties to the United States and its allies, and mainland countries lacking such cooperation,” said Susannah Patton.

KEY FINDINGS

• China, the United States, and middle powers such as Australia, Japan, and South Korea have increased defence engagement with Southeast Asian countries, as evidenced by a rise in defence agreements, dialogue mechanisms, and joint military exercises since 2017.
   
• Southeast Asian countries’ defence engagements with the United States and China have different objectives. Partnerships with the United States focus on developing capability and interoperability, whereas engagements with China primarily serve diplomatic and confidence-building purposes.
   
• While the United States remains the primary non-Southeast Asian defence and security partner in the region, China has established a more prominent presence in mainland Southeast Asia through sustained defence diplomacy and has made some gains in deepening defence ties with Indonesia and Malaysia.
   
• New defence cooperation initiatives from the United States and its allies focus largely on the Philippines, Indonesia, and Singapore. This trend risks leaving mainland Southeast Asia more reliant on cooperation with China and Russia, increasing the geopolitical divide within the Association of Southeast Asian Nations (ASEAN).

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