Why It Matters

U.S. allies and partners including Japan, the Philippines, South Korea and Taiwan have significant security and economic interests tied to the South China Sea. The heavily trafficked waters are also the site of overlapping territorial and maritime claims, increasingly militarized outposts and recurring confrontations between China and the Philippines.

The Big Picture

The core dispute hinges on competing maritime claims. The People's Republic of China asserts a dashed line encompassing approximately 62% of the South China Sea, though it has never definitively explained what the line signifies or what it means by "adjacent waters" in its sovereignty claims. The Spratly Islands are contested by the PRC, Taiwan, Vietnam, Malaysia, Brunei and the Philippines, with the PRC, Taiwan and Vietnam each claiming all of the approximately 200 islands.

A 2016 arbitral tribunal convened under the U.N. Convention on the Law of the Sea ruled that none of the land features in the Spratly Islands are capable of generating an exclusive economic zone. China declared the ruling null and void. The tribunal also ruled that China violated the Philippines' sovereign rights in its exclusive economic zone by interfering with Philippine fishing and petroleum exploration, constructing artificial islands and failing to prevent Chinese fishermen from operating there.

China has controlled Scarborough Shoal since 2012 and declared a nature reserve there in September 2025. Both the United States and the Philippines rejected the declaration as unlawful. China subsequently deployed a floating structure and buoys in and around Scarborough Shoal over Philippine protests.

China's artificial outposts in the Spratly Islands are equipped with advanced anti-ship and anti-aircraft missile systems. A Department of Defense report found that China's outposts enable the country to maintain a more flexible and persistent military and paramilitary presence in the South China Sea. Vietnam has also accelerated reclamation work since 2021, creating an estimated 4.3 square miles of artificial land.

The China Coast Guard and PRC maritime militia regularly harass and block Philippine Coast Guard and fishing vessels throughout the South China Sea. These confrontations have included the use of water cannons, collisions, ramming and other efforts to obstruct Philippine vessels.

The Bottom Line

The United States makes no territorial claim in the South China Sea and takes no position on sovereignty over geographic features there, but U.S. officials have urged that disputes be resolved without coercion and in accordance with international law.

The 2023 U.S.-Philippines Bilateral Defense Guidelines reaffirm that an armed attack in the Pacific, including anywhere in the South China Sea, on either country's armed forces, aircraft or public vessels, including Coast Guard vessels, would invoke mutual defense commitments under the 1951 Mutual Defense Treaty. The United States also maintains that international law protects freedom of navigation and overflight through exclusive economic zones, including for military ships and aircraft.

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