South China Sea

What it is

The South China Sea is a marginal sea of the western Pacific Ocean covering roughly 3.5 million km², bounded by China to the north, Vietnam to the west, the Philippines to the east, and Malaysia and Brunei to the south. It carries an estimated US$3.4 trillion in global trade annually (as of 2016, roughly 21% of all maritime commerce), supports fishing grounds that feed hundreds of millions of people across Southeast Asia, and sits above significant but disputed hydrocarbon reserves.

Six governments assert overlapping sovereignty: the People's Republic of China (PRC), Taiwan, Vietnam, the Philippines, Malaysia, and Brunei. China's claim is the most expansive. The "nine-dash line", a boundary tracing back to a 1947 map published by the Republic of China government, encloses roughly 90% of the sea and cuts through the EEZs of every other claimant.

History

Modern competition intensified after the 1982 United Nations Convention on the Law of the Sea (UNCLOS) codified exclusive economic zones extending 200 nautical miles from coastlines, overlapping with all claimants' positions. China ratified UNCLOS in 1996 but declined to formally reconcile the nine-dash line with the convention.

The dispute entered a new phase in 2012, when China seized Scarborough Shoal from the Philippines and barred Filipino fishermen from the area. Between 2013 and 2016, China carried out large-scale land reclamation on at least seven Spratly Island features, building military-grade runways and port facilities at Fiery Cross Reef, Subi Reef, and Mischief Reef. On 12 July 2016, a Permanent Court of Arbitration tribunal, in a case the Philippines filed in 2013, found China's historic rights claim under the nine-dash line incompatible with UNCLOS and determined that none of the Spratly high-tide features generate full EEZ entitlements. China rejected the award as "null and void." Taiwan, whose government originally drew the nine-dash line, also rejected it.

Current state

As of mid-2026, Scarborough Shoal is the active flashpoint. China has stationed vessels there continuously since 2012 and, in June 2026, installed floating barriers and a temporary research structure. The Philippines recorded 44 Chinese seacraft across four contested West Philippine Sea features in the week of 23-29 June. A naval standoff on 23 June 2026 brought Chinese and Philippine warships within roughly 90 metres of each other, the closest encounter in three years.

President Ferdinand Marcos Jr. has pursued a nature reserve designation for Scarborough Shoal to elevate the dispute in international law and draw in allied governments. The coast guard cooperation accord and the RIMPAC 2026 exercises reflect a consolidating US-led coalition posture across the broader western Pacific.

Relationships

China views control of the South China Sea as tied to denying the United States uncontested force projection into the western Pacific and securing energy-import sea lanes. The US conducts regular Freedom of Navigation Operations (FONOPs) to contest China's maritime claims and holds treaty obligations to the Philippines under the 1951 US-Philippines Mutual Defense Treaty. Japan has protested Chinese military activity near Yonaguni and contributes coast guard support to the Philippines. ASEAN and China adopted a Declaration on the Conduct of Parties in 2002 and launched formal Code of Conduct negotiations in 2017; no binding text has been agreed as of 2026, with China seeking language that would exclude third-party military involvement. The PLA's expanding carrier force has shifted the military balance undergirding all these negotiations.

What to watch

Whether China converts Scarborough Shoal into a permanent installation, replicating what it accomplished across the Spratlys from 2013 onward. The PCA ruling has no enforcement arm, but the Philippines consistently invokes it at the UN and in bilateral meetings; whether other claimants follow that legal strategy matters. The ASEAN Code of Conduct talks, where China's push to exclude external militaries collides with Philippine, Vietnamese, and Malaysian interests. And the trajectory of PLA exercise patterns around Taiwan: they signal the cost China believes it can impose on US intervention anywhere in the western Pacific, which sets the ceiling for all deterrence calculations in the South China Sea.