When Chinese maritime militia vessels were spotted swarming near Sandy Cay, a string of sandbars just off the coast of Pag-asa Island, in early 2023, tensions surged once again in the South China Sea. Unlike in previous years, the Philippines did not quietly lodge a diplomatic protest or downplay the encounter. Instead, under the leadership of President Ferdinand Marcos Jr., Manila issued a forceful condemnation and deployed additional coast guard patrols, signaling a significant break from its earlier, more restrained approach. This moment marked more than just a local confrontation, it was a flashpoint that captured a larger transformation in Philippine foreign policy.
Long at the center of overlapping maritime claims involving China, Vietnam, Malaysia, Brunei, and Taiwan, the South China Sea has evolved into a theater for regional power plays. The Philippines’ newly assertive stance is emerging as a game changer, realigning regional dynamics, challenging Beijing’s expansive claims, and reaffirming the role of international maritime law. As Manila positions itself at the forefront of defending the rules-based order in the Indo-Pacific, its evolving role could reshape the strategic contours of the region.

Table of Contents

Historical and Legal Basis of Philippine Claims

The Philippines’ claims in the South China Sea are not simply products of modern geopolitics, they are rooted in centuries of historical presence and legal continuity. One of the most notable historical references is the Velarde Map, an 18th-century Spanish-era document that depicts maritime features now known as part of the Kalayaan Island Group as being within Philippine territory. Long before formal nation-states were defined in Southeast Asia, Filipino fishermen from Palawan and other western coastal regions regularly sailed to and made use of features in the Spratlys for livelihood and navigation. These historical patterns of use reinforce a longstanding relationship between the Filipino people and the contested maritime zones.
The legacies of colonial administration further solidify the Philippines’ historical claim. Under Spanish rule, and later during American sovereignty, maritime territories west of Palawan were considered part of the Philippine archipelago. This was formalized through the Treaty of Paris (1898) and the Treaty of Washington (1900), which legally defined the territorial boundaries inherited by the Republic of the Philippines. The Kalayaan Island Group, in particular, was later explicitly claimed by the Philippines in 1978 through Presidential Decree No. 1596, citing historical, geographical, and legal justifications. It was declared an integral part of Palawan province and placed under Philippine administrative control, asserting a claim that has endured despite competing interests from other regional states.
The Philippines’ position in the South China Sea is further underpinned by strong legal foundations, particularly under international law. Chief among these is the United Nations Convention on the Law of the Sea (UNCLOS), to which the Philippines and China are both signatories. Under UNCLOS, the Philippines is entitled to a 200-nautical-mile Exclusive Economic Zone (EEZ), granting it sovereign rights over natural resources within that maritime expanse. This framework is central to Manila’s assertion that many of the contested features, including parts of the Spratly Islands and Scarborough Shoal, fall within its EEZ, making China’s expansive claims legally untenable.
The turning point came in 2016, when the Permanent Court of Arbitration (PCA) in The Hague ruled overwhelmingly in favor of the Philippines in its case against China. The ruling categorically rejected Beijing’s sweeping “nine-dash line” claim as inconsistent with international law and UNCLOS. Furthermore, the tribunal clarified the legal status of various features in the South China Sea, stating that most are either low-tide elevations or rocks incapable of generating their own EEZs. This landmark decision significantly bolstered Manila’s position, although China has refused to recognize or comply with the verdict.
Domestically, the Philippines has moved to solidify these maritime entitlements through new legislation. The Philippine Maritime Zones Act of 2023 and the Archipelagic Sea Lanes Act of 2024 clearly define the country’s maritime boundaries and establish navigational regimes, ensuring internal legal coherence with UNCLOS. As President Ferdinand Marcos Jr. declared during the signing of the latter law, “These laws are a testament to our resolve to safeguard our waters for future generations.” These measures signal not only legal clarity but also a renewed national commitment to asserting and defending maritime rights.
The geopolitical stakes are highest in three major flashpoints within Philippine-claimed waters: the Kalayaan Island Group, Scarborough Shoal, and Second Thomas Shoal. The Kalayaan Island Group, which forms part of the broader Spratly chain, hosts Philippine-occupied features such as Pag-asa Island, which now includes a modest civilian population and a military outpost. These islands and reefs are regularly patrolled and supplied by Philippine forces, but also face constant shadowing and harassment from Chinese vessels.

Tensions are equally persistent at Scarborough Shoal (Bajo de Masinloc), a rich fishing ground historically used by Filipino fishermen. Since a 2012 standoff, Chinese coast guard ships have maintained de facto control over the shoal, often barring Filipino boats from entering. Despite the PCA ruling declaring the shoal a traditional fishing area open to multiple states, Chinese encroachment continues unabated, fueling diplomatic clashes.
Perhaps the most dangerous standoff involves Second Thomas Shoal (Ayungin Shoal), where the Philippines maintains a symbolic outpost aboard the BRP Sierra Madre, a grounded navy vessel serving as a sovereignty marker. Chinese attempts to blockade resupply missions have led to multiple high-seas confrontations, including aggressive water cannoning and ramming incidents. Each clash raises concerns of inadvertent escalation between the two nations.
The most recent flashpoint, the Sandy Cay Incident of 2025, highlights the Philippines’ growing assertiveness. When Chinese officials claimed to have “dealt with” Philippine activities in the area, Manila quickly fired back, publicly denying Beijing’s version of events and asserting that Filipino operations in the area were lawful and ongoing. The incident sparked a series of high-level diplomatic exchanges, with the Philippine Department of Foreign Affairs stating unequivocally: “We will not be silenced nor deterred in defending our maritime rights.” This bold rhetoric, backed by continued patrols and legal positioning, reflects a broader shift in Manila’s posture, one rooted in history, international law, and an emerging sense of national urgency.

Recent Actions and Strategic Developments

President Marcos Jr. has championed a policy of “assertive transparency”, leveraging public diplomacy as a strategic tool. The Philippine government now routinely releases video footage of Chinese harassment, such as water cannon attacks and dangerous maneuvers, to global media outlets, shaping international opinion and exposing Beijing’s coercive behavior. At home, this approach has galvanized public support, with maritime sovereignty emerging as a rallying point for national unity and pride.
Chinese provocations have intensified, including laser targeting, ramming, and water cannon attacks against Philippine vessels. Despite this, the Philippines has maintained a policy of peaceful resistance paired with operational assertiveness, continuing resupply missions and patrols. In April 2025, China escalated tactics by deploying drones to shadow resupply missions, marking a new dimension in hybrid maritime intimidation.
Manila has filed over 45 diplomatic protests in 2024 alone, demonstrating a sustained legal and diplomatic campaign. It submitted a formal claim to the UN Commission on the Limits of the Continental Shelf (CLCS), seeking to extend its continental shelf in the West Philippine Sea. The Philippines also continues to invoke the 2016 arbitral ruling in international forums and alliance meetings, reinforcing its commitment to a rules-based maritime order.
The Armed Forces of the Philippines (AFP) launched Horizon 3 of its modernization program in 2025, focusing on maritime domain awareness, upgrading patrol aircraft, deploying surveillance drones, coastal radars, and new missile systems. Key allies—including the U.S., Japan, and South Korea, have pledged naval assets, including offshore patrol vessels (OPVs) and destroyers. The Enhanced Defense Cooperation Agreement (EDCA) now covers nine bases, strategically spread across Luzon and Palawan. Balikatan 2025, the largest joint exercise to date, included live-fire drills and a simulated island recapture, reflecting elevated preparedness.
To avoid unintended escalation, Manila and Beijing have increasingly utilized direct hotlines between defense and maritime agencies. A bilateral maritime dialogue mechanism, while under strain, remains in place. Provisional humanitarian resupply agreements, particularly at Second Thomas Shoal, have been established, though frequently violated by China, testing the limits of diplomatic engagement.
Regional and International Reactions

A. United States

The United States has emerged as the Philippines’ most vocal and committed ally in the South China Sea. Through regular Freedom of Navigation Operations (FONOPs), Washington has challenged China’s expansive claims and reinforced the principle of open sea lanes. In 2024, the U.S.-Philippines Mutual Defense Treaty was unequivocally reaffirmed, with U.S. officials pledging that any armed attack on Philippine public vessels or aircraft in the South China Sea would trigger a joint response. Support has also widened through the Quad alliance, with Japan, Australia, and India increasingly aligning with Manila’s legal position and providing diplomatic backing in multilateral forums.

B. ASEAN Neighbors

Reactions within ASEAN remain mixed, reflecting divergent strategic alignments. Vietnam and Malaysia, though cautious in tone, quietly endorse the Philippines’ reliance on international law and the 2016 arbitral ruling, seeing parallels in their own maritime disputes with China. In contrast, Cambodia and Laos continue to tilt toward Beijing, often obstructing stronger ASEAN consensus on the issue. Efforts to finalize a long-delayed ASEAN Code of Conduct in the South China Sea have stalled, largely due to China’s insistence on excluding external powers like the U.S. from any enforcement mechanism, an approach Manila opposes.

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C. China’s Reaction

China remains steadfast in rejecting the 2016 arbitral ruling and continues to push for “dual-track” diplomacy, which marginalizes U.S. involvement and favors one-on-one negotiations with Southeast Asian claimants. In response to Manila’s assertive posture, Beijing has escalated disinformation efforts, targeting President Marcos Jr. and the Philippine military through state-backed media and social platforms. Notably, a wave of cyberattacks on Philippine government agencies in early 2025 was attributed to Chinese actors, signaling a shift to more covert and hybrid forms of pressure.
Strategic Implications and Future Outlook
The intensifying maritime and aerial encounters in the South China Sea have significantly raised the risk of miscalculation or accidental conflict. With coast guard vessels, naval ships, drones, and aircraft operating in close proximity, even minor incidents could rapidly escalate. The region’s critical freedom of navigation, vital for over $3 trillion in global trade annually, is under threat as commercial shipping routes come under increased Chinese surveillance and harassment, challenging the security of international sea lanes.
Amid these tensions, the Philippines has emerged as a strategic linchpin in the Indo-Pacific. By combining legal assertiveness with active diplomatic and military partnerships, Manila is redefining its role from a peripheral claimant to a central actor in the defense of international maritime law. Its stance serves as a model for smaller states confronting larger powers, proving that international norms, when actively upheld, can counterbalance coercive strategies. Through consistent engagement with multilateral institutions and its alliance network, the Philippines is increasingly viewed as both a moral and legal leader in resisting Chinese expansionism.

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Future Scenarios

Entrenchment: The most likely scenario involves continued Chinese pressure, met by expanding support from allies such as the U.S., Japan, Australia, and the EU. The Philippines will likely deepen defense ties, accelerate modernization, and play a larger regional security role.
De-escalation: A less probable path would see a breakthrough in ASEAN-China negotiations producing a robust Code of Conduct, but only if China agrees to binding mechanisms and inclusivity. Without substantive concessions, this remains unlikely.
Regional Solidarity: A more dynamic and evolving outcome could be the informal alignment of maritime Southeast Asian states, like Vietnam, Indonesia, and Malaysia—with backing from the Quad and EU. This alignment would not be a formal bloc but a coalition of interest, centered on preserving the rules-based order and resisting unilateral coercion.

Conclusion

The Philippines’ assertive stance marks a geopolitical inflection point in the enduring South China Sea dispute. By shifting from quiet diplomacy to active resistance, Manila has not only recalibrated its national policy but also reshaped the regional security discourse. While this approach carries significant risk, including the potential for confrontation, it has injected new momentum into the defense of international law, freedom of navigation, and sovereign rights in contested waters.
More than a tactical shift, the Philippines’ strategy represents a broader normative stand, a powerful example of how small and medium-sized states can leverage legal tools, alliances, and transparency to challenge coercion by great powers. As global attention turns increasingly to the Indo-Pacific, Manila’s balancing act between sovereignty, deterrence, and diplomacy may come to define the contours of the region’s evolving security architecture.
In standing firm, the Philippines is not only defending its waters, it is helping chart a course for a rules-based maritime order, one that could empower like-minded nations across the Indo-Pacific to stand their ground with both principle and resolve.