China Primer: South China Sea Disputes

Congressional Research Service | Dolven, Ben; Piekos, William

The People's Republic of China continues to assert expansive sovereignty claims over roughly 62 percent of the South China Sea, deploying coast guard vessels, floating barriers, and military infrastructure across contested land features. These maritime operations directly challenge neighboring claimants—including the Philippines, Vietnam, Malaysia, Brunei, and Taiwan—while threatening crucial international sea lanes that carry up to one-third of global ship-borne trade and host 3.6 billion barrels of oil.

Tensions stem from competing interpretations of the 1994 UN Convention on the Law of the Sea, with Beijing rejecting the 2016 arbitral tribunal ruling that invalidated its dashed-line claims. Flashpoints have intensified around Scarborough Shoal and Second Thomas Shoal, where China maintains persistent coast guard deployments. Beijing routinely blocks Philippine resupply operations. In response, Washington has expanded security assistance through the Pacific Deterrence Initiative under the FY2026 National Defense Authorization Act to reinforce regional maritime domain awareness.

Comment

China's employment of gray-zone tactics at Second Thomas Shoal tests the operational threshold of the 1951 U.S.-Philippines Mutual Defense Treaty without triggering armed conflict. By deploying floating barriers and coast guard blockades around the grounded BRP Sierra Madre, Beijing exposes the friction between non-lethal coercion and formal security guarantees. This dynamic forces Manila to calibrate routine resupply missions while testing the updated Bilateral Defense Guidelines established in 2023.

The resulting operational strain directly affects how the United States Indo-Pacific Command allocates surveillance capabilities under the Pacific Deterrence Initiative. Consequently, maintaining deterrence across the West Philippine Sea relies on continuous maritime domain awareness feeds coordinated through the Quadrilateral Security Dialogue at Scarborough Shoal.

Strategic Question for Discussion

If Chinese gray-zone tactics surrounding the BRP Sierra Madre continue to avoid triggering formal armed attack thresholds, how does that affect the operational deterrence model established under the 1951 U.S.-Philippines Mutual Defense Treaty?

The pattern suggests that non-lethal blockades create strategic ambiguity that delays formal treaty activation while incrementally shifting control over disputed features. Available evidence points toward Manila relying increasingly on shared intelligence under the Pacific Deterrence Initiative to counter coercion short of military conflict. My assessment is that deterrence will depend less on traditional capital ship deployments and more on persistent, multilateral maritime domain awareness.

Share your assessment in the comments below.

To read in details click here