Legal Disputes in the South China Sea: The "Nine-Dash Line"

The South China Sea is not only a vital maritime corridor through which approximately 30% of global sea trade passes, but also a region of immense strategic value due to its natural resources, fishing grounds, and military significance. However, this area has become a hotspot for legal and geopolitical disputes, primarily due to China’s assertion of the so-called “nine-dash line.” This claim, which lacks clear legal foundations under international law, has triggered objections from several Southeast Asian countries and drawn attention to the limits of historical rights in maritime law.

This article examines China’s “nine-dash line” from the perspective of the 1982 United Nations Convention on the Law of the Sea (UNCLOS), analyzes the 2016 ruling of the Permanent Court of Arbitration (PCA) in detail, discusses the legal ambiguity surrounding Taiwan’s position, and outlines the objections raised by ASEAN claimants. The analysis is grounded in treaty provisions, arbitral jurisprudence, and state practice.

Relevant Provisions of UNCLOS: Territorial Sea, EEZ, Continental Shelf

UNCLOS provides a structured legal framework for maritime zones. It defines a territorial sea extending up to 12 nautical miles from the coast, where the coastal state exercises full sovereignty. Beyond this, it establishes the Exclusive Economic Zone (EEZ), which stretches up to 200 nautical miles, granting the coastal state sovereign rights to explore and exploit marine resources. Furthermore, the continental shelf may extend up to 350 nautical miles based on the natural prolongation of the landmass.

These legal classifications are based on objective geographical and legal criteria, rather than on historical claims. As such, UNCLOS prioritizes measurable and verifiable parameters over vague or unilateral assertions rooted in historical narratives.

The "Nine-Dash Line" Claim and Its Legal Assessment

China's "nine-dash line" claim is based on alleged historical rights over most of the South China Sea. However, this claim is inconsistent with the legal framework established by UNCLOS. First, UNCLOS does not recognize historical rights as a valid basis for maritime entitlements unless expressly provided in the Convention, which it is not. Second, the "nine-dash line" lacks clarity; it has never been formally defined through geographic coordinates and does not correspond to any recognized legal maritime zone.

Therefore, under international law, particularly the regime established by UNCLOS, China’s claim fails to meet the legal standards required for maritime delimitation. It also undermines the principle of predictability and legal certainty, which are essential in the application of international maritime law.

The 2016 PCA Award: Philippines v. China

In 2016, the Permanent Court of Arbitration in The Hague delivered a landmark ruling in response to the case brought by the Philippines against China. The Tribunal found that China’s “nine-dash line” had no legal basis under UNCLOS and that any historical rights claimed by China had been extinguished upon the entry into force of the Convention.

The Tribunal also held that most of the maritime features in the Spratly Islands, including Scarborough Shoal, are rocks or low-tide elevations that do not generate an EEZ. It concluded that China had violated the Philippines’ sovereign rights by interfering with its EEZ and by constructing artificial islands within it. Although China refused to participate in the proceedings and rejected the ruling, the Tribunal emphasized that China, as a party to UNCLOS, is bound by the Convention and its dispute resolution mechanisms.

This ruling clarified the legal status of features and claims in the South China Sea and reaffirmed UNCLOS as the primary legal instrument governing maritime entitlements.

Taiwan’s Legal Status and Response

Taiwan controls Itu Aba (Taiping Island), the largest natural feature in the Spratly Islands, and claims it qualifies as an island capable of generating its own EEZ. However, Taiwan’s legal position is complicated by its unique status in international law. It is not a member of the United Nations and is not a party to UNCLOS, which limits its formal legal standing in maritime disputes under the Convention.

The PCA in 2016 held that Itu Aba does not meet the criteria of an “island” under Article 121 of UNCLOS, as it cannot sustain a stable human community or economic life of its own. Taiwan strongly rejected the ruling, arguing that it undermined its sovereignty and mischaracterized the nature of Itu Aba. Nonetheless, its objections have received limited international support due to its ambiguous legal status as a non-recognized state actor.

Positions and Claims of ASEAN Countries

Several Southeast Asian states, particularly the Philippines, Vietnam, Malaysia, and Brunei, have voiced opposition to China’s expansive maritime claims. The Philippines, having won the 2016 arbitral case, uses the ruling as a diplomatic tool to assert its rights and rally international support. Vietnam also rejects China’s claims over the Paracel and Spratly Islands, maintaining its own entitlements based on coastal geography.

Malaysia and Brunei have taken more cautious approaches but have submitted maps and claims to the United Nations that indirectly challenge China’s position. Overall, these countries rely on UNCLOS as the legal foundation for their maritime claims and call for multilateral diplomacy and adherence to international law in resolving disputes.

Legal Assessment: Implications for International Law

The current dispute underscores several important principles of international law. UNCLOS remains the primary legal regime governing maritime zones and entitlements. Claims such as the “nine-dash line,” which are vague and lack legal basis under the Convention, cannot override treaty-based entitlements. The 2016 PCA award, though not enforceable in a traditional sense, has significant legal and normative value. It reinforces treaty obligations and contributes to the development of customary international law by clarifying state rights and obligations.

Furthermore, state practice in the region—especially the legal positions and actions of ASEAN countries—strengthens the normative weight of the PCA ruling and weakens the legal credibility of China’s assertions.

Conclusion: Legal and Diplomatic Outlook

The South China Sea dispute is not merely a regional maritime issue but a critical test for the authority of international law. The 2016 PCA ruling provides a legal framework centered on UNCLOS, yet its effectiveness depends on the willingness of states to comply with international norms. China’s refusal to recognize the award and its continued assertive presence in disputed waters expose the tension between law and power in international relations.

Moving forward, durable resolution may require sustained multilateral engagement, robust legal diplomacy, and the strengthening of international legal institutions. Ultimately, the future of the South China Sea will hinge not only on legal clarity but also on political will and respect for the rule of law.