For years, the South China Sea has been viewed as a potential flashpoint in the growing geopolitical rivalry between China and the United States.
Southeast Asian states are often presented as small powers caught in a storm.
However, this picture is changing, as a new and nuanced security network is taking shape across the region.
It is built not around formal alliances but around access deals, missile sales, coast guard exercises, intelligence-sharing talks and defense consultations.
On June 1, the Philippines and Vietnam upgraded relations to an upgraded strategic partnership and signed a memorandum on defense cooperation that commits them to high-level exchanges, strategic dialogue, information sharing and joint activities at sea.
The partnership builds on previous Coast Guard arrangements, including hotlines and mechanisms to prevent incidents.
pile of defense deals
Late last month, Indian officials said New Delhi had signed a $629 million (€555 million) deal to supply the BrahMos supersonic cruise missile system to Vietnam.
Vietnam is the second Southeast Asian buyer publicly confirmed by India after the Philippines, which has signed a $375 million contract for three BrahMos batteries in 2022. The missiles have been jointly developed by India and Russia.
Meanwhile, Japan’s security ties with the Philippines have become quite solid. A reciprocal access agreement came into force last September, expanding troop deployments in each country, while this month they began talks about a new deal to share classified defense information.
In February, Australia and Indonesia signed the “Jakarta Treaty”, a general security treaty that commits both governments to regular top-level consultations.
There is absolutely no united front against China
Neither of these agreements creates a NATO-style alliance. However, together they show how middle powers are trying to make unilateral pressure at sea difficult and costly.
Hunter Marston, director of the Southeast Asia program at the Lowy Institute, told DW that all of these countries share concerns about China and have an interest in maintaining the rule of law at sea and keeping the region free from pressure from great powers.
At the same time, they recognize, to varying degrees, the possibility that the US could reduce its commitments to regional security, which would bring instability and unpredictability to the existing balance of power, he said.
Marston said, “Although they do not all share an eye on regional security or equally support the United States military presence, now is the time for the middle powers to unite in their interests. No one is strong enough to do this alone.”
“Even Indonesia and India, which are major powers in their own right, are looking at each other to enhance their security.”
The rise of multilateral deterrence
The Philippines has progressed the fastest. Since President Ferdinand Marcos Jr. entered office in 2022, Manila has become more willing to publicize Chinese pressure in the South China Sea and broaden defense cooperation beyond its main ally, the United States.
Manila and Hanoi still have their own maritime claims, yet both face Chinese pressure in the South China Sea and have an interest in preventing disputes from being resolved by force or intimidation.
The upgrade of their relationship this month reflects that calculation. In 2024, their coast guards conducted their first joint exercise. This month’s agreements go even further, linking defense cooperation to maritime law, humanitarian assistance, counter-terrorism and peacekeeping.
The upgrade “affirms Vietnam’s unique and enduring position as the Philippines’ sole strategic partner in Southeast Asia,” Marcos Jr. was quoted as saying at the signing ceremony in Manila.
preservation of strategic autonomy
India, on the other hand, has a different role. New Delhi is not a claimant to the South China Sea and its rivalry with China focuses on the Himalayan border and parts of the Indian Ocean. But the BrahMos deal further strengthens its “Act East” policy.
For Hanoi, the missile system strengthens coastal defenses and complicates any naval or coast guard operations near its shores. For New Delhi, this shows that its Indo-Pacific policy is no longer just about diplomacy and trade. It is also about defense exports, maritime security and strategic signalling.
Kei Koga, associate professor in the public policy and global affairs program at Nanyang Technological University, told DW that despite Vietnam’s public disputes with China, particularly in the maritime domain, Hanoi remains cautious, seeking to maintain strategic autonomy and avoid formal alignment.
“India’s BrahMos deal with Vietnam fits this pattern, as it strengthens Vietnam’s own deterrence and coastal defense capability without making Vietnam part of an anti-China coalition,” he said.
Indonesia is still more cautious. Jakarta does not describe itself as being in a territorial dispute with Beijing. But China’s sweeping claims match the waters around the Natuna Islands, and Indonesian officials know the problem is more than just theoretical.
Japan and Australia join the equation
Tokyo was once more cautious about security cooperation in Southeast Asia because of constitutional limits on what its military could do. However, this is changing now.
The Japan–Philippines Reciprocal Access Agreement was the first agreement of its kind that Tokyo had concluded with a Southeast Asian country. Tokyo and Manila began talks this month on a Common Security of Military Information Agreement, which would allow the secure exchange of classified defense information and ease future transfers of Japanese military equipment.
“The Japan-Philippines Reciprocal Access Agreement is a remarkable example because it makes defense cooperation not just symbolic, but more functional,” Koga said.
Australia’s Jakarta Treaty with Indonesia, signed in February, points in this direction. It is not a mutual defense treaty and does not oblige either side to fight for the other. But it creates a habit of consultation at the top of government and provides a framework for cooperation between the two sides if regional situations deteriorate.
Trust in America is waning
China remains the largest trading partner of most Southeast Asian countries and an important economic partner for Japan, Australia and India, making regional players wary of antagonizing Beijing.
These expanded defense partnerships are “still loose, flexible and uneven, with no unified command structure or formal collective-defense commitment, because these frameworks do not demand any obligations or commitments,” Koga said.
They are “primarily about strengthening each state’s own capabilities, rather than creating a system in which they remain dependent on others for their national defense.”
At the same time, recent deals indicate that “spokespeople are becoming increasingly unified in their perception of the threat and their willingness to commit money to combat it,” Marston said.
He said doubts about the credibility of the United States are increasing throughout the region. So, “we’re seeing a more decentralized and multilateral approach to security, which is probably a good thing in the long run.”
The story of the South China Sea does not stop about China and the United States. But now it is also about the middle powers learning to work around the limitations of both.
Edited by: Srinivas Majumdaru