The South China Sea Territorial Disputes: Claims, Law, and Geopolitics

The South China Sea is a 1.4 million-square-mile marginal sea of the western Pacific Ocean that hosts one of the world's most complex and consequential territorial disputes. Bounded by the Southeast Asian mainland, Taiwan, and the Philippines, the waterway is a critical artery for global commerce and a flashpoint for geopolitical competition.[13]

Six governments—China, Vietnam, the Philippines, Malaysia, Brunei, and Taiwan—claim overlapping sovereignty over the sea's islands, reefs, and the maritime zones they generate. The disputes center primarily on the Spratly and Paracel island chains, where competing historical narratives and interpretations of international law have led to military standoffs and decades of diplomatic friction.[2][5]

At the heart of the tension is the asymmetry between the sweeping claims of the People's Republic of China and the legal entitlements asserted by smaller littoral states. As the United States and other global powers assert their own interests in freedom of navigation, the local disputes have escalated into a broader structural contest over the rules governing international waters.[5][9]

The Geographic and Economic Stakes

The South China Sea is an indispensable conduit for global trade, connecting the Indian Ocean to the western Pacific. According to the Center for Strategic and International Studies, an estimated $3.4 trillion in commerce transited the waterway in 2016, representing roughly 21 percent of all global trade.[11]

For regional economies, the reliance on these shipping lanes is even steeper. Nearly 40 percent of China's total trade passes through these waters, alongside massive volumes of energy imports bound for Japan, South Korea, and Taiwan. The high concentration of commercial goods flowing through narrow chokepoints like the Strait of Malacca makes the sea a vital strategic vulnerability.[11]

Energy resources further elevate the sea's strategic value. The U.S. Energy Information Administration estimates that the South China Sea holds approximately 11 billion barrels of untapped oil and 190 trillion cubic feet of natural gas in proved and probable reserves. State-owned enterprises in claimant nations frequently clash over the rights to explore these lucrative hydrocarbon blocks.[5][8]

Beyond hydrocarbons, the sea supports a vital and heavily exploited fishing industry. The coastal fringes are home to roughly 270 million people, and the waters provide a primary source of protein for the region's dense population. The Indo-West Pacific biogeographic province is one of the world's most diverse shallow-water marine areas, hosting 70 recognized coral genera.[13][14]

However, the U.S. Geological Survey notes that overlapping claims have hindered cooperative environmental management. The lack of a unified regulatory regime leaves the marine biota vulnerable to severe over-exploitation, pollution, and habitat destruction, with coral reefs suffering extensive damage from dredging and destructive fishing practices.[14]

The Historical Origins of the Claims

The modern disputes are rooted in the aftermath of World War II, when the withdrawal of Japanese forces left a power vacuum in the region. In 1947, the Republic of China published a map featuring an eleven-dash line that claimed the majority of the sea. After the Chinese Communist Party took power in 1949, it adopted a revised nine-dash line.[5]

China's claims are the most expansive, encompassing approximately 85 percent of the South China Sea. The Ministry of Foreign Affairs of the People's Republic of China maintains that Chinese activities in the sea date back over 2,000 years. Beijing argues that its sovereignty over the islands and their adjacent waters is supported by abundant historical and legal evidence.[5][6]

Vietnam fiercely contests China's narrative, claiming historical sovereignty over both the Paracel and Spratly islands. Hanoi asserts that it has actively ruled both island chains since the 17th century, possessing historical documents from the Nguyen dynasty to support its administrative control long before the modern era.[2][5]

The Philippines asserts jurisdiction over a portion of the Spratlys it calls the Kalayaan Island Group. This claim stems from a 1956 expedition by a Philippine citizen, Tomas Cloma, who declared the islands newly discovered territory. Manila formally incorporated the area in 1978, basing its claims on proximity and the principle of terra nullius.[2][5]

Malaysia and Brunei claim specific features and maritime zones that fall within their respective exclusive economic zones, drawn from their coastlines on the island of Borneo. Unlike the historical arguments advanced by China and Vietnam, the claims of Malaysia and Brunei rely strictly on the modern international legal framework governing maritime boundaries.[2][5]

The Legal Framework of UNCLOS

The primary legal framework governing these maritime disputes is the United Nations Convention on the Law of the Sea (UNCLOS). Negotiated between 1973 and 1982, the treaty entered into force in 1994 and serves as the constitution for the world's oceans, establishing rules for maritime zones and resource management.[10][12]

Under UNCLOS, coastal states are granted a 12-nautical-mile territorial sea where they exercise full sovereignty. Beyond that, states can claim a 200-nautical-mile exclusive economic zone (EEZ) where they hold sovereign rights to explore and exploit natural resources in the water column and the seabed.[10]

A critical distinction in UNCLOS is the difference between islands and rocks. Article 121 stipulates that only a naturally formed area of land capable of sustaining human habitation or an economic life of its own can generate a 200-nautical-mile EEZ. Rocks that do not meet this standard generate only a 12-nautical-mile territorial sea.[1]

The United States played a major role in negotiating UNCLOS but has never ratified the treaty, largely due to domestic political opposition regarding deep seabed mining provisions. However, Washington formally recognizes the treaty's navigational and jurisdictional provisions as customary international law and insists that all nations, including China, must abide by them.[9][10]

The 2016 Arbitral Tribunal Ruling

In January 2013, the Philippines initiated compulsory arbitration against China under Annex VII of UNCLOS, challenging the legality of the nine-dash line. The Permanent Court of Arbitration in The Hague convened an ad hoc tribunal to hear the case. The Philippines asked the tribunal to clarify the maritime entitlements of specific features in the Spratlys.[1]

China refused to participate in the proceedings. Beijing argued that the tribunal lacked jurisdiction because the core issue was territorial sovereignty, which falls outside the treaty's scope. China also cited a 2006 declaration it made under UNCLOS Article 298, opting out of compulsory dispute settlement for maritime boundary delimitations.[1][5]

On July 12, 2016, the tribunal issued a sweeping, unanimous ruling in favor of the Philippines. It concluded that China's claim to historic rights within the nine-dash line had no legal basis under UNCLOS. The tribunal ruled that any historical rights China may have had were extinguished when it signed the convention.[1][5]

The tribunal also evaluated the status of the features in the Spratly Islands. It determined that none of the features, including the largest natural formations like Itu Aba, meet the legal definition of an island capable of generating a 200-nautical-mile EEZ. Consequently, the tribunal found that China had violated the Philippines' sovereign rights by operating within the Philippine EEZ.[1]

Beijing immediately rejected the 2016 award as "null and void." The Chinese government issued a statement reiterating its sovereignty over the islands and their adjacent waters, insisting that the arbitration was a political farce orchestrated to contain China's rise. While the ruling is legally binding on both parties, there is no international police force to compel compliance.[1][5][6]

Physical Occupation and Island Building

The physical occupation of the South China Sea features is highly fragmented. According to the Asia Maritime Transparency Initiative, Vietnam occupies at least 21 features in the Spratlys, the Philippines occupies nine, China controls seven, Malaysia holds five, and Taiwan administers one.[3][5]

The scramble to occupy these features began in earnest in the 1970s following the discovery of offshore oil potential. China entered the Spratlys relatively late, seizing its first features in 1988 after a deadly naval skirmish with Vietnam at Johnson South Reef. In 1995, China took control of Mischief Reef from the Philippines.[5]

To solidify its claims and overcome its late entry, China engaged in an unprecedented campaign of island-building starting in 2013. Beijing deployed massive dredging vessels to pump millions of tons of sand onto seven submerged reefs in the Spratlys, creating over 3,200 acres of new artificial land.[3]

The U.S. Department of State regularly publishes "Limits in the Seas" reports detailing how these artificial islands do not generate legal maritime zones under international law. UNCLOS explicitly states that artificial islands, installations, and structures do not possess the status of islands and have no territorial sea of their own.[4][10]

The dredging campaign caused catastrophic damage to the surrounding marine ecosystems. The 2016 arbitral tribunal found that China's island-building activities had caused severe, permanent harm to the coral reef environment and violated its obligation to preserve fragile marine ecosystems under UNCLOS.[1]

Militarization and Asymmetric Tactics

The material alteration of the environment has fundamentally shifted the regional balance of power. The Asia Maritime Transparency Initiative tracks the militarization of these outposts, noting that China has constructed deep-water ports, radar facilities, reinforced bunkers, and military-grade runways on Fiery Cross, Subi, and Mischief Reefs.[3]

These fortified outposts allow the People's Liberation Army Navy to maintain a continuous, pervasive presence across the South China Sea. They serve as forward operating bases that extend the reach of Chinese air and naval power deep into Southeast Asia, complicating the strategic calculations of rival claimants and the United States.[5][9]

Alongside conventional naval forces, Beijing relies heavily on the Chinese Coast Guard and the People's Armed Forces Maritime Militia. These ostensibly civilian fleets operate in the gray zone below the threshold of armed conflict, using asymmetric tactics like swarming, water cannons, and ramming to enforce China's jurisdictional claims.[5]

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This pervasive presence routinely disrupts the economic activities of other claimant states. For years, Malaysia, the Philippines, and Vietnam have faced intense harassment when attempting to prospect for hydrocarbons or conduct routine resupply missions to their own outposts within their claimed exclusive economic zones.[5]

Great Power Competition and U.S. Involvement

The United States views the preservation of the rules-based order in the South China Sea as a vital national interest. The Congressional Research Service notes that U.S.-China strategic competition in these waters is driven by Washington's commitment to freedom of navigation and Beijing's desire to secure its near seas against perceived encirclement.[9]

To demonstrate its position, the U.S. Navy conducts regular Freedom of Navigation Operations (FONOPs). These operations involve sailing warships near contested features to challenge what Washington terms "excessive maritime claims" and to assert the right of innocent passage under international law.[9]

Beijing routinely condemns these patrols as provocative acts that undermine regional stability and infringe on Chinese sovereignty. The Chinese military frequently shadows U.S. vessels, leading to tense maritime encounters that elevate the risk of an accidental collision escalating into a broader geopolitical crisis.[5][9]

The United States also maintains a Mutual Defense Treaty with the Philippines, signed in 1951. Washington has repeatedly clarified that an armed attack on Philippine armed forces, public vessels, or aircraft in the South China Sea would invoke U.S. mutual defense commitments, directly linking local territorial disputes to great power deterrence.[9]

ASEAN and the Elusive Code of Conduct

Diplomatic efforts to manage the disputes have yielded limited structural progress. In 2002, China and the Association of Southeast Asian Nations (ASEAN) signed the Declaration on the Conduct of Parties in the South China Sea. The non-binding agreement committed the signatories to resolve their disputes peacefully and to refrain from inhabiting presently uninhabited features.[7]

For over two decades, ASEAN and China have negotiated toward a binding Code of Conduct to replace the 2002 declaration. Progress has been halting, stalled by fundamental disagreements over the code's geographic scope, its legal enforceability, and whether it should restrict the military activities of outside powers.[5][7]

ASEAN's consensus-based decision-making model has frequently been strained by the disputes. Because any single member can veto a joint statement, Beijing has successfully leveraged its economic influence over non-claimant states like Cambodia to prevent the bloc from issuing unified condemnations of Chinese actions in the sea.[5]

In the absence of a binding resolution mechanism, the structural reality of the dispute remains entrenched. Without established incident management protocols or a shared interpretation of maritime law, the South China Sea remains a volatile arena where the limits of international law are continually tested by the realities of state power.[5][9]