Geopolitics › Southeast Asia & Oceania
South China Sea disputes
China's line since 1947; 2016 ruling· Conflict or rivalry
DisputedContested claims, borders or interpretations.
Overlapping claims by China and five other governments to islands, reefs and waters of a sea carrying an estimated $3 trillion of trade a year.
See it on the Geopolitics map →The picture
China's 'nine-dash line' covers about 90% of the sea. Vietnam claims the Paracel and Spratly islands; the Philippines, Malaysia and Brunei claim areas off their coasts; Taiwan's claim mirrors China's. China built about 3,200 acres of artificial islands in the Spratlys in 2013–16 and armed them with runways and missiles. A 2016 tribunal rejected China's sweeping claims; Beijing ignores the ruling. Flashpoints include Scarborough and Second Thomas shoals, where Chinese and Philippine vessels clash with water cannon and rammings.
Why it matters
Fish, undersea oil and gas, and shipping lanes are at stake, and a clash with the Philippines could pull in the US through its defense treaty.
Key facts and numbers
Satellite imagery from CSIS's Asia Maritime Transparency Initiative, the 2016 arbitral award, claimants' UN filings and coast guard video. Trade estimates vary by method.
What to watch
Disputed: China has never defined what the line legally claims, the waters or only the features, and ASEAN–China talks on a code of conduct remain unfinished.
Inside this (1)
Connections (6)
▸China (People's Republic of China) claims most of South China Sea disputesFact
The relationship
China claims nearly everything inside its 'nine-dash line', about 90% of the sea, citing historic rights. It backs the claim with artificial islands, the world's largest coast guard and a maritime militia that block, ram and water-cannon rival ships, plus legal steps such as a 2025 nature reserve declared at Scarborough Shoal.
Since when and why
The line was first drawn by the Republic of China in 1947; the People's Republic kept it and built its island bases in 2013–16 under Xi Jinping.
How we know
China's 2009 map filed with the UN, official statements, and satellite imagery of its bases tracked by CSIS's Asia Maritime Transparency Initiative.
What to watch
Debated: whether China aims mainly at fish, oil and gas, at control of sea lanes, or at a protected bastion for its nuclear-missile submarines based on Hainan; analysts weigh these motives differently.
▸Vietnam contests China's claims in South China Sea disputesFact
The relationship
Vietnam claims both the Paracel and Spratly islands and holds 21 Spratly features, more than any other claimant. South Vietnam lost the Paracels to China in a 1974 battle, and in 1988 China seized Johnson South Reef, where 64 Vietnamese sailors died. Vietnam has recently built over 2,000 acres of new land, second only to China.
Since when and why
Paracels, January 1974; Johnson South Reef, March 1988; current building at Barque Canada Reef and other Spratly outposts.
How we know
Satellite imagery from CSIS's Asia Maritime Transparency Initiative, historical records of the clashes and Vietnamese diplomatic protests.
What to watch
Why Beijing reacts more quietly to Vietnam's island-building than to Philippine resupply missions; analysts cite party-to-party ties and Hanoi's lack of a US alliance.
▸Strait of Malacca funnels shipping into the waters of South China Sea disputesFact
The relationship
Ships leaving the Strait of Malacca northbound enter the South China Sea to reach Chinese, Korean, Japanese and Taiwanese ports. That makes the two one route: much of East Asia's oil and trade must cross waters where China, Vietnam, the Philippines and others dispute islands and reefs.
Since when and why
From Singapore northeast past the Spratly and Paracel islands toward Hong Kong, Taiwan and Shanghai.
How we know
Ship-tracking data and US EIA estimates show most Malacca traffic continuing through the South China Sea; the geography itself is not in dispute.
What to watch
Whether China's island bases could threaten shipping in a war, and how much trade really transits; the common $3 trillion estimate varies by method.
▸ASEAN (Association of Southeast Asian Nations) hosts code-of-conduct talks on South China Sea disputesFact
The relationship
ASEAN and China signed a non-binding Declaration on the Conduct of Parties in 2002 and have negotiated a code of conduct since 2013, aiming to finish by 2026 under the Philippine chair. Consensus rules let members close to Beijing water down statements; in 2012 ASEAN failed to issue a communiqué over the issue.
Since when and why
Phnom Penh, 2002 and 2012; talks across ASEAN capitals since 2013; Philippine chairmanship, 2026.
How we know
The 2002 declaration, ASEAN–China joint statements setting the 2026 target, and summit communiqués.
What to watch
Whether the code will be legally binding, cover the disputed areas or constrain China at all; claimants and China disagree on all three.
▸South China Sea disputes is a flashpoint in US–China strategic rivalryWidely agreed
The relationship
China claims most of the sea and has built and armed artificial islands; the US rejects the claims and sails warships through in 'freedom of navigation' operations. Washington's 1951 defense treaty with the Philippines, whose ships clash with China's coast guard, could draw the US into a fight.
Since when and why
The Spratly and Paracel islands, Scarborough Shoal and Second Thomas Shoal; island-building in 2013–16; regular US operations since 2015.
How solid?
US Navy announcements, Chinese protests, Philippine coast guard video, and US statements that the treaty covers Philippine ships anywhere in the sea.
What to watch
Disputed: China says it defends historic rights and calls US patrols provocations; the US and other claimants cite the 2016 ruling. What would trigger the treaty is unclear.
▸Ferdinand Marcos Jr. pushes back on China in South China Sea disputesFact
The relationship
Marcos replaced quiet diplomacy with publicity: coast guard ships carry journalists and release videos of Chinese water cannon and rammings. He signed a 2024 law defining Philippine maritime zones, keeps resupplying the grounded outpost at Second Thomas Shoal, and leans on US and Japanese backing. Clashes continued into July 2026.
Since when and why
Mainly Second Thomas and Scarborough shoals, since 2023; Maritime Zones Act signed November 8, 2024; coast guard spokesman Jay Tarriela leads the publicity.
How we know
Philippine Coast Guard footage, Chinese Coast Guard statements giving rival accounts, and the Maritime Zones Act.
What to watch
Disputed: Beijing says Manila provokes it with US backing; Manila says it defends its legal rights. Whether publicity deters China or raises risk is debated.