The US-China Summit and the ADMM-Plus Maritime Security Joint Exercise: Analysis and Implications for South Korea

Executive Summary

Separately from the symbolic achievements of the US-China summit in Washington on September 24–25—namely, the extension of the trade truce and the establishment of an AI crisis communication channel—the ADMM-Plus Maritime Security Joint Exercise, co-hosted by the Philippines and Japan, took place in the West Philippine Sea during the same week. In this exercise, which involved 11 vessels from eight countries, China attended only the opening ceremony and avoided the sea phase, while its standoffs with the Philippines continued near Scarborough Shoal and Second Thomas Shoal. This demonstrates that the ASEAN-centric multilateral framework is transforming into a venue for building interoperability between regional countries and extra-regional partners while excluding China. This trend coincides with an asymmetric restructuring driven by US resource constraints, which shifts the burden to allies, expands exercises along the US-Japan-Australia axis, and relatively scales back those along the US-South Korea axis. Rather than viewing participation through a binary lens, South Korea needs to design a phased response system based on a baseline scenario, determining at which level and under what justification it should engage.

I. Issue Analysis

Issue Analysis: Philippine-Led ADMM-Plus Maritime Security Joint Exercise and Tensions in the West Philippine Sea

1. Background and Progress

The multinational maritime security joint exercise in the West Philippine Sea is not an isolated event. It is an extension of the military modernization and security partnership expansion policies that the Philippines has pursued since the inauguration of the Marcos administration [4]. The US-Philippines Mutual Defense Treaty marked its 75th anniversary on September 30, and around this time, the Philippines has increased the frequency of joint exercises and the number of accessible bases with extra-regional partners, including the United States and Japan [4]. Japan's first-ever live-fire drill of its Type 12 surface-to-ship missile outside its own territory during the Balikatan exercise in May this year also aligns with this trend [7].

During the same period, standoffs recurred near Scarborough Shoal and Second Thomas Shoal (Ren'ai Jiao) between the Philippine Coast Guard and Navy and the China Coast Guard and People's Liberation Army Navy (PLAN). On September 18, a collision occurred between a Philippine vessel and the China Coast Guard vessel Sanzhouao, which the Global Times characterized as a "deliberate provocation" by the Philippine side [8]. Within the Philippines, some interpret these clashes as Chinese pressure linked to plans for the militarization of Palawan [5]. The ADMM-Plus Experts' Working Group on Maritime Security (EWG-MS) joint exercise differs in character, as it was conducted under the multilateral framework of ASEAN amid this accumulation of bilateral friction.

2. Current Situation

According to a report by Rappler, 11 vessels from eight countries participated in the exercise, which focused on interoperability among regional navies, medical evacuation, search and rescue, and assistance to stranded vessels [1]. Although China attended the opening ceremony, it did not participate in the actual sea phase of the exercise [1]. In effect, China maintained its status as an ADMM-Plus member state while opting out of practical maritime cooperation.

Around the same time the exercise was underway, the Philippine Coast Guard announced that its resupply mission to the grounded warship at Second Thomas Shoal was obstructed by dangerous maneuvers from the Chinese side. Commodore Jay Tarriela, spokesperson for the Philippine Coast Guard, stated, "There was no collision and no injuries, but the dangerous maneuvers of the China Coast Guard created a serious risk of collision" [3]. The Philippine Coast Guard characterized the actions of the China Coast Guard and the PLAN as "obstructing a lawful humanitarian assistance and resupply operation" [3]. Conversely, the Global Times described the same incident from the opposite perspective, reporting that the China Coast Guard blocked the Philippines' "illegal" resupply attempt, which it claimed was conducted without prior authorization [6]. The factual narratives constructed by Manila and Beijing regarding the same incident are in direct conflict.

3. Key Actors and Positions

The Philippines is the host country of this exercise and the frontline party. Manila seeks to utilize the ASEAN-centric multilateral framework of ADMM-Plus to lend regional legitimacy to its position on the South China Sea. At the same time, it is pursuing economic and cultural cooperation with Taiwan, with its Department of Foreign Affairs stating that its One-China policy remains "consistent, clear, and unchanged" [11]. This dual-track approach—simultaneously expanding security partnerships and managing relations with Beijing—is a key factor that provokes pushback from Beijing [9].

China frames this exercise and the Philippines' broader foreign policy moves as containment efforts. A Global Times editorial described Japan's support for the Philippines as an "ambition to break free from the constraints of its pacifist constitution" and cast Japan as a "regional proxy" serving the US-Japan alliance [8]. Zhu Fenglian, spokesperson for the Taiwan Affairs Office, criticized the maritime cooperation between Taiwan's Democratic Progressive Party (DPP) authorities and the Philippines as "extremely despicable" [10]. By maintaining minimal formal engagement through attendance at the opening ceremony while abstaining from the actual sea phase, China can be seen as signaling its refusal to recognize the legitimacy of the ADMM-Plus framework.

Japan views its support for the Philippines as a key pillar of its security partnership diversification. This is an extension of the relaxation of constraints on Japan's security policy following the revision of the Three Principles on Transfer of Defense Equipment and Technology and the decision to acquire counterstrike capabilities [4]. While the United States seeks to bind its relationship with the Philippines into a multilateral network, leveraging the symbolism of the 75th anniversary of their mutual defense treaty, the Global Times argues that such "joint defense" fails to provide the Philippines with genuine resilience [4].

Philippine domestic public opinion diverges in some respects from the government's hardline stance toward China. According to a Pew Research Center survey cited by the South China Morning Post (SCMP), 47% of Filipinos aged 18 to 34 viewed China favorably; while some described the South China Sea clashes as "disappointing," they blamed the United States for high inflation [12]. This gap between the government's expansion of security partnerships and the sentiments of the youth indicates that the Marcos administration's China policy does not enjoy absolute domestic support.

4. Key Issues

First is the conflict over the construction of facts. The announcements from the Philippines and China regarding the resupply mission to Second Thomas Shoal define the same event in diametrically opposed terms, making it difficult to rely on either narrative in isolation without third-party verification [3][6].

Second is the functional shift of the ASEAN-centric ADMM-Plus framework. China's decision to attend only the opening ceremony and opt out of the maritime exercise aligns with observations that this framework is being restructured into a space for institutionalizing maritime cooperation between ASEAN and extra-regional partners [1].

Third is the potential for expanded friction stemming from the Philippines' dual-track approach. Maintaining a One-China policy while simultaneously pursuing practical cooperation with Taiwan structurally invites pushback from China [9][10][11].

Fourth is the vulnerability of the domestic public opinion base. As the government's hardline stance toward China diverges from youth opinion, the long-term sustainability of this policy is likely to be tested in future elections [12].

II. In-Depth Analysis

In-Depth Analysis: Structural Implications of the Philippine-Led ADMM-Plus Maritime Security Joint Exercise

1. Root Cause Analysis

The root cause of the joint exercise culminating in "maritime cooperation without China" lies in the legal deadlock over territorial disputes in the South China Sea. The Philippines asserts the legitimacy of its maritime activities within its exclusive economic zone (EEZ) based on the 2016 Permanent Court of Arbitration (PCA) ruling. China has consistently maintained its position of refusing to recognize this ruling. This fundamental gap has not been narrowed through bilateral dialogue, as evidenced by the direct clash between Manila and Beijing in their factual constructions of the Second Thomas Shoal resupply. The Philippine Coast Guard characterized the China Coast Guard's maneuvers as "dangerous" obstruction [3]. Conversely, the Global Times defined the same resupply attempt as an "illegal" act conducted without prior authorization and described the Chinese interception as legitimate law enforcement [6]. In the absence of agreement on the basic facts of the incident, the trust-building function of bilateral channels cannot operate.

Amid this deadlock, the path chosen by the Philippines has been to multilateralize the issue. Manila has projected its South China Sea position onto the ASEAN-centric multilateral framework of ADMM-Plus, attempting to reframe bilateral friction as a matter of regional legitimacy. China's decision to attend the opening ceremony but abstain from the sea phase [1] can be read as a passive rejection of this multilateralization effort. By choosing to both attend and abstain, Beijing sent a dual signal: maintaining its status as a member state while drawing a line at practical cooperation.

2. Structural Context

Security Structure: The Transformation of ASEAN Centrality

ADMM-Plus was originally designed as a framework for ASEAN to maintain balance by engaging regional major powers. However, this case demonstrates that the actual operation of the framework is diverging from its design intent. With China—the largest stakeholder in the South China Sea—absent from the maritime exercise involving 11 vessels from eight countries, the ASEAN multilateral framework has transformed into a venue for regional countries and extra-regional partners to build interoperability while excluding China [1]. This transformation is not confined to the Philippines. A similar pattern is evident in the expansion of the US-Japan-Australia joint exercise, "Oriental Shield 26." An asymmetry is unfolding where exercises along the Japan-Australia-India axis are expanding while those along the US-South Korea axis are being shortened—a product of the US decision to offset its resource constraints by shifting the burden to allies [4]. The continuous expansion of the US-Philippines defense agreement in the South China Sea direction [4] also aligns with this structural trend.

Political Structure: Manila's Dual-Track Approach and the Gap in Domestic Public Opinion

The Philippine Department of Foreign Affairs reaffirmed that its One-China policy is "consistent, clear, and unchanged," while stating that it will continue economic and cultural cooperation with Taiwan [11]. This dual-track approach has translated into practical cooperation, as seen in the transfer of decommissioned patrol vessels from Taiwan's Coast Guard Administration to serve as Philippine law enforcement vessels [10]. The Chinese side characterized this as an act undermining the "One-China" principle, with the spokesperson for the Taiwan Affairs Office issuing a direct statement of criticism [10]. Chinese experts warned that the Philippines' engagement with Taiwan would add a new source of friction to the South China Sea issue [9].

However, this expansion of security partnerships does not enjoy the support of Philippine public opinion as a whole. According to the Pew Research Center survey, 47% of young Filipinos aged 18 to 34 hold a favorable view of China, and some respondents, while viewing the South China Sea clashes as "disappointing," blamed the United States for rising energy prices [12]. The existence of a gap between the security elite's alignment with the US and Japan and the youth's perception of China suggests that Manila's multilateral security policy does not rest on an unconditional domestic political foundation.

Economic and Identity Structure: Militarization of Palawan and Resource Pressure

Philippine domestic security experts interpret the recent increase in threats to civilian vessels by the China Coast Guard in connection with plans for the militarization of Palawan. They argue that Chinese provocations are continuing as a reaction to ongoing plans to fortify Palawan [5]. If this interpretation is correct, the maritime clashes are a surface manifestation of structural competition over long-term economic and strategic interests, namely securing resources and sea lanes in the South China Sea. This means the issue is not of a nature that can be resolved through short-term incident management.

3. Historical Precedents and Comparative Case Analysis

This is not the first instance of China selectively withdrawing from an ASEAN multilateral framework. However, the signal in this case is clearer than before, as it was bifurcated into attending the opening ceremony and abstaining from the practical exercise. China chose to draw a line only at practical cooperative content while avoiding a direct rejection of the legitimacy of the multilateral framework itself. This is a strategy with lower management costs than complete withdrawal.

During the same period, Indonesia's actions showed a contrasting pattern. The Indonesian Navy conducted a joint navigation exercise with the PLAN in the waters east of Taiwan, after which the two countries agreed to expand military cooperation and launch a five-year action plan [2]. This pattern is assessed as "conditioned hedging" arising from Indonesia's structural dependence on China driven by its nickel downstreaming policy [2]. The Prabowo administration is employing a dual strategy of maximizing practical benefits while maintaining non-aligned rhetoric [2]. This represents hedging in the exact opposite direction of the Philippines' alignment with the US and Japan. The fact that the Philippines and Indonesia, despite both being ASEAN member states, are tracing opposite trajectories in defining their relations with China highlights the structural limitations that prevent ASEAN from forming a unified front against China. It is in this context that experts assess that Indonesian-style hedging is unlikely to spread uniformly to South China Sea claimants like the Philippines and Vietnam, and that any expansion is highly probable to unfold in a fragmented manner with varying speeds across countries [2].

There are also points of comparison with the pattern of normalizing gray-zone pressure in the Taiwan Strait. The PLAN's repeated ocean-going training, where training ships port in Indonesia following visits to Russia, Vietnam, and Brunei [2], is pointed out as a pattern that combines military alignment with ASEAN countries with regular entry into waters near Taiwan [2][8]. This indicates that the strategic grammar employed by China in the distinct geographical arenas of the South China Sea and the Taiwan Strait shares a similar structure.

4. Key Variables Shaping Future Developments

The first variable is the gap between the US approach to China and the pace of restructuring the regional security architecture. The unpredictability of the Trump administration is acting as a pressure forcing Asian allies to reassess their independent security postures [7]. If the asymmetry continues—where the United States pursues managed stability in Washington while the burden of independent exercises on allies and partners increases—the self-reliant networking among regional countries, including the Philippines, could accelerate.

The second variable is the direction of Philippine domestic politics and public opinion. How the gap between the security elite's alignment with the US and Japan and the youth's favorable perception of China [12] manifests in future election cycles will determine the sustainability of Manila's multilateral security policy.

The third variable is whether the linkage between the Taiwan issue and the South China Sea issue deepens. As cooperation between the Philippines and Taiwan expands, the intensity of China's pushback is also likely to increase [9][10]. If this linkage solidifies, the South China Sea has the potential to be redefined beyond an independent territorial dispute into an extension of the strategic landscape of the Taiwan Strait.

The fourth variable is the pace of differentiation in the hedging strategies of individual ASEAN member states. Unless Indonesian-style conditioned hedging spreads to other member states, ASEAN will maintain a structure that makes it difficult to speak with a unified voice on China-related issues [2]. If this differentiation solidifies, multilateral frameworks like ADMM-Plus are highly likely to increasingly harden into "minilateral cooperative bodies without China."