UNCLOS under Pressure: Assessing the Legality of Territorial Claims and Military Activities in the South China Sea
Adediran Babajide, President/CEO
Carlsron Initiative for Peace and Human Rights (CIPEHR)
Scope: International maritime law and global governance; legality of territorial claims and military activities under UNCLOS in the South China Sea and their implications for regional stability.
Abstract
The South China Sea represents one of the most complex maritime disputes in modern international relations. While the United Nations Convention on the Law of the Sea (UNCLOS) was designed to establish a comprehensive legal order for oceans, overlapping territorial claims and military activities by regional and external powers have tested its credibility. This article examines the legality of sovereignty claims, the militarization of artificial islands, and the exercise of navigation rights in light of UNCLOS provisions and the 2016 Philippines v. China arbitral award. It also reviews the key maritime zones—territorial sea, contiguous zone, exclusive economic zone (EEZ), continental shelf, and high seas—under international law. The study argues that the erosion of compliance with UNCLOS undermines the rule-based maritime order and threatens regional stability.
1. Introduction
The South China Sea dispute has evolved into a geopolitical flashpoint involving China, the Philippines, Vietnam, Malaysia, Brunei, Indonesia, and external actors such as the United States. The region’s strategic importance—rich in resources, vital trade routes, and military significance—makes it a key testing ground for the robustness of international maritime law.
The United Nations Convention on the Law of the Sea (UNCLOS), adopted in 1982, provides a “constitution for the oceans” (Churchill & Lowe, 2022). However, the rising disregard for its provisions, particularly by China’s expansive “nine-dash line” claim, has placed the Convention under strain. This article explores the theoretical and legal framework of maritime zones, evaluates the legality of regional territorial and military practices, and assesses the implications for international law and global governance.
2. Theoretical and Legal Framework under UNCLOS
Territorial Sea
The territorial sea extends up to 12 nautical miles from a coastal state’s baseline, granting full sovereignty, subject to the right of innocent passage for foreign vessels (UNCLOS, 1982, Arts. 2–3). States may regulate navigation, fishing, and environmental protection within this zone. In the South China Sea, overlapping territorial seas around disputed features such as the Spratly and Paracel Islands exacerbate tensions, especially when artificial islands are claimed to generate territorial seas—a position inconsistent with Article 121(3), which excludes rocks incapable of sustaining human habitation from generating such zones.
Contiguous Zone
Beyond the territorial sea, a contiguous zone extends up to 24 nautical miles from the baseline, where a state may enforce laws related to customs, taxation, immigration, and sanitation (Art. 33). This limited enforcement jurisdiction is designed to protect coastal interests without infringing on freedom of navigation (Kraska, 2011).
Exclusive Economic Zone (EEZ)
The EEZ, extending up to 200 nautical miles, grants a state sovereign rights to explore and exploit natural resources, both living and non-living, in the water column and seabed (Art. 56). However, it does not confer full sovereignty; other states retain freedoms of navigation and overflight. In the South China Sea, China’s expansive claim based on historical maps conflicts with UNCLOS-defined EEZ boundaries of other littoral states (Bateman, 2023). The arbitral tribunal in Philippines v. China (2016) concluded that China’s claim to historic rights beyond its EEZ had no legal basis.
Continental Shelf
The continental shelf comprises the seabed and subsoil of the submarine areas extending beyond the territorial sea to the outer edge of the continental margin, or 200 nautical miles where the margin does not extend that far (Art. 76). States have exclusive rights to exploit mineral and other non-living resources. Continental shelf claims often overlap with EEZ disputes, particularly where hydrocarbon reserves are concerned (Zou, 2021).
High Seas
The high seas lie beyond any state’s jurisdiction and are open to all for navigation, fishing, scientific research, and cable laying (Art. 87). Freedom of the high seas is subject to obligations of due regard and peaceful use. Militarization of disputed waters near the high seas boundary undermines these principles (Klein, 2022).
Artificial Islands and Military Activities
Artificial islands, installations, and structures do not possess territorial seas of their own and do not affect delimitation (Art. 60). However, China’s construction of military installations on submerged reefs, such as Fiery Cross Reef, challenges this principle and raises questions about the militarization of international waters (Beckman, 2023).
3. The South China Sea Dispute under International Law
China’s “Nine-Dash Line” and Historic Rights
China’s nine-dash line encompasses nearly 90% of the South China Sea, based on vague historical claims. The 2016 Permanent Court of Arbitration (PCA) in Philippines v. China ruled that such claims are inconsistent with UNCLOS, which supersedes historical rights not expressly recognized (PCA Case No. 2013–19). The tribunal clarified that features like Mischief Reef and Subi Reef are low-tide elevations and thus incapable of generating EEZs or territorial seas (Permanent Court of Arbitration, 2016).
Sovereignty over Islands and Reefs
UNCLOS does not resolve issues of sovereignty over land territory, but it determines how maritime zones are generated. The Spratly Islands consist of numerous small features, most of which do not meet Article 121’s requirements for islands. States such as the Philippines, Vietnam, and Malaysia have constructed outposts on features they occupy, further complicating delimitation (Schofield, 2022).
Freedom of Navigation and Military Operations
Freedom of navigation operations (FONOPs), primarily by the United States, aim to challenge excessive maritime claims. China regards such operations as violations of sovereignty, while the U.S. argues they uphold UNCLOS principles. This clash underscores differing interpretations of “innocent passage” and “military activities” in EEZs (Yoshihara & Holmes, 2023).
ASEAN’s Role and Code of Conduct
The Association of Southeast Asian Nations (ASEAN) has pursued a Code of Conduct for the South China Sea since 2002. However, progress remains slow due to divisions among members and Chinese influence. Regional diplomacy has thus failed to enforce legal obligations or prevent escalation (Thayer, 2024).
4. Challenges to the UNCLOS Regime
Non-Compliance and Great Power Politics
The South China Sea disputes reveal UNCLOS’s vulnerability to non-compliance by powerful states. China’s refusal to accept the 2016 arbitral ruling highlights a broader challenge: UNCLOS lacks enforcement mechanisms beyond diplomatic and reputational consequences (Ku, 2022). This raises concerns about the durability of international law in the face of realpolitik.
Militarization and Environmental Damage
China’s large-scale land reclamation and military fortification have caused irreversible environmental damage to coral reefs and marine ecosystems. The PCA tribunal found that China violated Articles 192 and 194 of UNCLOS, which require states to protect and preserve the marine environment (Permanent Court of Arbitration, 2016; Symmons, 2024).
Freedom of Navigation and Airspace
Tensions have expanded to the aerial domain, with China declaring an Air Defense Identification Zone (ADIZ) over parts of the sea. Such practices, although not governed by UNCLOS, conflict with its spirit of open and peaceful seas (Beckman, 2023).
Regional and Global Security Implications
The dispute threatens not only regional stability but also global trade, as nearly 30% of world shipping passes through the South China Sea (UNCTAD, 2024). Persistent militarization could escalate into conflict, undermining international confidence in the rule-based order.
5. The Future of the Law of the Sea
Reforming UNCLOS is difficult due to the consensus-based amendment process and differing state interests. However, strengthening dispute resolution mechanisms, expanding environmental accountability, and enhancing regional cooperation through ASEAN and international courts are possible steps forward (Huang, 2025). Moreover, promoting legal education and capacity-building among smaller coastal states can empower them to assert rights under international law.
6. Conclusion
The South China Sea dispute encapsulates the tension between international law and power politics. While UNCLOS remains the cornerstone of maritime order, its authority is increasingly undermined by strategic competition, non-compliance, and militarization. The 2016 arbitral award reaffirmed the legal clarity of UNCLOS, yet enforcement remains elusive. Sustaining the rule of law at sea will depend on collective adherence, regional cooperation, and renewed commitment to the principles of peaceful coexistence and environmental stewardship.
UNCLOS, though under pressure, continues to represent the best hope for balancing sovereignty, resource rights, and global maritime peace.
References
Bateman, S. (2023). Maritime security in the South China Sea: Law, policy, and power politics. Routledge.
Beckman, R. (2023). The 2016 South China Sea arbitration: Impact on regional stability and maritime law. Ocean Development & International Law, 54(2), 101–123.
Churchill, R. R., & Lowe, A. V. (2022). The law of the sea (5th ed.). Manchester University Press.
Huang, X. (2025). Revisiting the South China Sea Code of Conduct: Prospects for a rules-based order. Asian Journal of International Law, 15(1), 1–25.
Klein, N. (2022). Freedom of the high seas and the new geopolitics of maritime power. International Affairs, 98(4), 857–873.
Kraska, J. (2011). Maritime power and the law of the sea: Expeditionary operations in world politics. Oxford University Press.
Ku, C. (2022). Power and principle in the South China Sea arbitration. Journal of International Dispute Settlement, 13(1), 1–20.
Permanent Court of Arbitration. (2016). The South China Sea arbitration (The Republic of the Philippines v. The People’s Republic of China), PCA Case No. 2013–19.
Schofield, C. (2022). The South China Sea disputes: Sovereignty, resources, and international law. Hart Publishing.
Symmons, C. (2024). Environmental obligations under UNCLOS: The case of the South China Sea. Marine Policy, 155, 105739.
Thayer, C. A. (2024). ASEAN and the South China Sea: Balancing unity and autonomy. Contemporary Southeast Asia, 46(1), 59–82.
UNCTAD. (2024). Review of maritime transport 2024. United Nations Conference on Trade and Development.
Yoshihara, T., & Holmes, J. R. (2023). Red star over the Pacific: China’s rise and the challenge to U.S. maritime strategy (3rd ed.). Naval Institute Press.
Zou, K. (2021). The continental shelf in the South China Sea: Legal and geopolitical issues. Ocean Development & International Law, 52(3), 223–242.
