The South China Sea Disputes: Geography, Resources, and Rival Claims

A Sea Worth Fighting Over

Approximately $3.4 trillion in trade passes through the South China Sea annually — about one-third of global maritime commerce. The sea covers roughly 3.5 million square kilometers between the southern coast of China, the island of Borneo, the Malay Peninsula, and the Philippines. Beneath its waters lie an estimated 11 billion barrels of oil and 190 trillion cubic feet of natural gas, though commercial extraction has proven difficult. Its fisheries support the livelihoods of an estimated 3.7 million fishermen from surrounding countries. And at the center of four sets of overlapping territorial claims sit scattered archipelagos of tiny islands, reefs, and atolls, most uninhabitable, all intensely contested — including through military force.

No other body of water outside the Arctic concentrates as many unresolved sovereignty disputes, as much strategic military attention, and as much commercial value in such constrained geography. The South China Sea is simultaneously an economic artery, a contested commons, and the frontline of the 21st century's most consequential strategic rivalry.

The Claims and the Nine-Dash Line

Six governments claim portions of the South China Sea: China, Vietnam, the Philippines, Malaysia, Brunei, and Taiwan. Their claims overlap significantly, and the legal basis for each varies considerably.

China's nine-dash line — a U-shaped boundary enclosing nearly the entire sea, first published on a Chinese map in 1947 and inherited by the People's Republic in 1949 — is the most expansive and most disputed claim. The line extends hundreds of kilometers beyond China's continental shelf, encompassing waters that UNCLOS (the United Nations Convention on the Law of the Sea, which China has ratified) assigns as Exclusive Economic Zones of Vietnam, the Philippines, Malaysia, and Brunei.

The 2016 Arbitral Tribunal Ruling

The Philippines filed for international arbitration in January 2013 under UNCLOS Annex VII, challenging China's nine-dash line and specific Chinese actions around Philippine-claimed features. China refused to participate in the proceedings and rejected the tribunal's jurisdiction.

The Permanent Court of Arbitration ruled in July 2016 — decisively, in 501 pages — that China's nine-dash line had no legal basis under UNCLOS, that China had violated Philippine sovereign rights in its EEZ, and that most of the contested features were legally "rocks" or "low-tide elevations" entitled to only limited maritime zones rather than full EEZ entitlements. The ruling was the most comprehensive international legal determination ever issued on South China Sea disputes.

China declared the ruling "null and void" and continued its activities. The US endorsed the ruling but is not itself a party to UNCLOS (having not ratified it), creating the irony of America defending a legal regime it has never formally joined. No enforcement mechanism exists under international law to compel compliance.

Artificial Islands: Creating Facts on the Water

China's most consequential strategic action in the South China Sea has been its artificial island construction program, conducted primarily between 2014 and 2016. Using sand dredging equipment, China reclaimed approximately 3,200 acres (1,295 hectares) of land on seven reefs in the Spratly Islands — features that were previously submerged or barely above water at high tide — and constructed military installations including runways, hangars, radar systems, and surface-to-air missile batteries.

• Fiery Cross Reef now hosts a 3,125-meter runway capable of landing any aircraft in China's military inventory, a deepwater harbor, and facilities for approximately 200–300 military personnel.
• Mischief Reef, within the Philippine Exclusive Economic Zone under the 2016 ruling, was occupied by China in 1995 (initially with fishing shelters, now a full military base).
• Subi Reef features the largest airstrip in the Spratlys — 3,000 meters — with barracks and communication facilities.
• The construction gave China forward military presence within range of key sea lanes, Vietnamese ports, the Philippine coast, and the Strait of Malacca approaches.

The islands transformed the strategic calculus. Before 2014, China's military reach in the southern Spratlys required ships to operate at extended range from Hainan Island. The artificial bases eliminated that constraint, allowing sustained presence and dramatically complicating any military response by rivals or the United States.

Freedom of Navigation and US Military Operations

The United States does not take a position on the specific sovereignty of contested islands, but it conducts Freedom of Navigation Operations (FONOPs) — deliberate transits within 12 nautical miles of disputed features — to challenge excessive maritime claims and uphold the principle that the sea is international waters. The US conducted at least 8 FONOPs in the South China Sea in 2022 alone, drawing Chinese protests and occasional shadowing by PLA Navy vessels.

China's military response has included increasingly assertive intercepts of US aircraft and vessels. In May 2023, a Chinese fighter aircraft conducted an unnecessarily aggressive intercept of a US RC-135 reconnaissance aircraft over the South China Sea, passing within 400 feet at high speed — one of dozens of such incidents in a pattern of escalating tactical harassment that stops short of direct conflict.

ASEAN and the Fractured Response

The Association of Southeast Asian Nations (ASEAN), which includes claimants Vietnam, the Philippines, Malaysia, and Brunei alongside non-claimant members, has failed to present a unified response to China's assertiveness. ASEAN's consensus requirement means China's ally Cambodia (and sometimes Laos and Myanmar) can block collective statements critical of Chinese behavior.

• The 2012 ASEAN Summit in Phnom Penh, Cambodian-hosted, ended for the first time in ASEAN's 45-year history without a joint communiqué because Cambodia blocked language on South China Sea disputes.
• A Code of Conduct for the South China Sea has been under negotiation between China and ASEAN since 2002. As of 2024, no agreement has been reached on whether it will be legally binding or what geographic scope it covers.
• Vietnam has been the most assertive ASEAN member in resisting China — expanding its own presence on Spratly features and filing legal protests — while simultaneously managing an economically essential bilateral relationship with Beijing.

The South China Sea dispute has no clean resolution pathway. China's artificial islands represent territorial facts that cannot be undone without force. The 2016 legal ruling established China's historical rights claim as legally invalid but has no enforcement mechanism. ASEAN's internal divisions prevent coordinated pressure. And the US-China relationship — simultaneously economically interdependent and strategically competitive — makes either American military enforcement or accommodation equally problematic as policy options.

What happens in the South China Sea will help define whether 21st-century international order is governed by legal norms and multilateral institutions or by the power of major states to create facts on the ground — and water — regardless of legal determinations.