The South China Sea and the Philippines Defense Strategies 

The Diplomat author Mercy Kuo regularly engages subject-matter experts, policy practitioners, and strategic thinkers across the globe for their diverse insights into U.S. Asia policy. This conversation with Su Mon and Tomas Buenaventura – Asia Pacific senior analyst and senior research assistant, respectively, at ACLED (Armed Conflict Location and Event Data) – is the 523rd in “The Trans-Pacific View Insight Series.â€

Examine the South China Sea conflict escalation environment based on ACLED data.

ACLED data reveals the South China Sea security environment is increasingly defined by the normalization of gray zone tactics and rapid militarization. A persistent state of confrontation significantly escalated in the first half of 2026, with a roughly 490 percent increase in Chinese force movements between January and June compared to the previous six months. This activity is concentrated within the Philippines' Exclusive Economic Zone (EEZ), specifically around Scarborough Shoal, Sabina Shoal, and Thitu Island.

This uptick in force movements — including survey vessels, China Coast Guard (CCG) deployments, and maritime militia — is often accompanied by more frequent encounters, ranging from harassment and blocking maneuvers to competing law enforcement operations. These activities are not just about presence, but about altering the status quo on the seas. They represent a coordinated effort to advance territorial claims and consolidate control, keeping tensions high while strategically averting open military conflict. 

Essentially, the region has become a primary theater for power projection, where the margin for error is shrinking, and the risks of a miscalculation that could lead to broader instability are becoming more acute.

How are gray zone tactics affecting the chance of escalation in the South China Sea?

The real danger with gray zone operations is not necessarily that they will spark an immediate war; it's that they gradually normalize coercion. By using persistent, incremental actions — such as the routine deployment of maritime militia and coast guard vessels — Beijing is steadily shifting the status quo, redefining “normal†maritime activity in a way that feels manageable daily but creates significant long-term strategic shifts.

ACLED's South China Sea Monitor suggests that these gray zone operations are expanding into cyber warfare, intelligence operations, and suspected sabotage against critical infrastructure. This expansion shows the growing imbalance between China and other claimant states, necessitating stronger cooperation among regional partners and allies to respond effectively.

Ultimately, this creates a dangerous environment where the primary risk is not a deliberate decision to go to war, but a miscalculation. As these tactics become more sophisticated, they blur strategic intent and erode the trust needed to manage crises. Regional security and coordination mechanisms, such as the South China Sea Code of Conduct negotiations, have not kept pace with these developments, leaving a widening gap in governance, making the region increasingly vulnerable to unintended escalations.

Identify key developments in the Scarborough Shoal and the Spratly Islands.

The situation at Scarborough Shoal has remained tense since China established de facto control there in 2012, despite the feature falling within the Philippines' EEZ. Beijing has maintained a constant presence, with the CCG and maritime militia frequently blocking, ramming, and using water cannons against Philippine vessels. Tensions intensified after Beijing designated the shoal a national “nature reserve†in September 2025 — a move China framed as environmental protection, but which Manila viewed as an attempt to consolidate administrative control. Subsequent reports of floating barriers, buoys, and a temporary research platform further heightened tensions, culminating in confrontations on July 23-24, 2026, when the CCG again deployed water cannons against Philippine government vessels.

The Spratly Islands present a more complex, multilayered security environment involving competing claims from Brunei, China, Malaysia, the Philippines, Taiwan, and Vietnam. The challenge here is twofold: immediate flashpoints and gradual, strategic military expansion. Second Thomas Shoal remains one of the most volatile flashpoints. While an informal arrangement since mid-2024 has reduced interference with routine Philippine resupply missions to the BRP Sierra Madre, China continues to block construction materials intended to strengthen the outpost. The recent clash on July 22 at Second Thomas demonstrates that both sides are contending over what constitutes acceptable military presence. 

Developments at Scarborough Shoal and the Spratly Islands reflect a broader contest, as China and the Philippines test resolve and respond to perceived encroachments. Each side is enforcing its own red lines, but in doing so is edging closer to crossing the other's.

Analyze how the United States-Philippines Mutual Defense Treaty (MDT) could draw Washington into a broader regional conflict. 

The Mutual Defense Treaty (MDT) signed by Manila and Washington in 1951 obligates both countries to come to each other's defense in case of an armed attack on either in the Pacific region. As the treaty's scope explicitly identified armed attacks as the trigger to both sides' defense obligations, this has given rise to the widespread use of “gray zone†tactics on China's part in its assertion of its maritime territorial claims against the Philippines. This seemingly hard limit for China's South China Sea activity allows Beijing to pressure Manila on its claims while keeping the risk of armed conflict with the U.S. at bay. Still, the very nature of gray zone tactics at sea — consisting of close vessel confrontations, tailing and blocking actions, and other delicate maneuvers — means that the risk of a lethal accident is never zero. 

Already, this July, a widely publicized confrontation between Chinese and Philippine personnel near Second Thomas Shoal left a Philippine soldier injured after being struck with a wooden baton. Even in this high-profile incident, though, no side has risked employing any sort of actual firepower against each other, as that would be indisputably escalatory and definitely be a notch above the confrontations of recent years — and likely enough reason for the U.S. to consider a heightened presence in the waters. 

Assess the current gray zone conditions between the Philippines and China. 

Despite the heated rhetoric between Manila and Beijing, the Philippines and China continue to engage each other very closely through diplomatic channels. Nevertheless, the tense environment created by the constant gray zone operations provides a conducive environment for potential triggers to MDT defense obligations, say, a lethal incident that leads both Chinese and Philippine forces to reach for firepower. In such a situation, the Philippines would count on the U.S. to make good on its repeated affirmations of its “ironclad†commitment to the Philippines' defense. 

For the time being, however, neither the Philippines and China seem to have any real desire to engage each other in armed conflict, especially given the otherwise close economic ties between the two countries. Thus, as long as the gray zone activities are managed to a tolerable degree, no matter how feisty the rhetoric gets between Manila and Beijing, they are currently unlikely to draw the U.S. into a conflict in the region.