Spotted in early January 2025 off the coast of the Philippines, a Chinese coast guard patrol follows the “nine-dash line”. This intimidation tactic reflects the international tensions in the South China Sea over Chinese claims in the region. Tensions for which international law is trying to provide solutions.
Deployed up to 55 miles off the coast of the Philippines, a Chinese patrol worries authorities. On 14 January, Jonathan Malaya, spokesman for the Philippine National Security Council, said that the Philippines, “alarmed” by this “growing threat”, “will not accept these intimidation tactics by stepping back.” In the South China Sea, China claims a maritime area often referred to as the “nine-dash line” under the pretext of its history and past influence in the region. The nine-dash line first appeared on Chinese maps in 1947. With this line, China claims 90% of the South China Sea. This maritime area is strategic because of the immense amount of resources (12% of the world’s fisheries reserves, 11 billion barrels of oil and more than 5 trillion cubic meters of natural gas) and the shipping routes that cross it (30% of world maritime trade). For these reasons, the Philippines, Vietnam, Brunei, Malaysia and Taiwan also claim part of this sea in accordance with the 1982 Montego Bay Convention. Since 2013, China has established numerous military bases on the Spratleys Islands to expand its exclusive economic zone (EEZ). It has also developed violent tactics to pressure the islands controlled by its neighbours. This led to numerous clashes between the coast guard. In 2016, the Permanent Court of Arbitration (PCA) ruled in favour of the Philippines, invalidating the nine-dash line and refusing to extend the Chinese EEZ. But China, which does not recognize the jurisdiction of the PCA, has rejected this decision. Because of their stakes, Maritime borders are often the origin of different international. Disputes that the International Court of Justice (ICJ) is regularly called upon to decide.
ICJ and maritime boundary disputes: a legal perspective
The ICJ was established in 1945 by the Charter of the United Nations. Its role is to settle the legal differences between states if they have consented. The various cases may concern military activities, air incidents, the delimitation of land and sea borders, etc. The ICJ can also give its opinion on legal questions submitted to it by the bodies of the United Nations (UN) or other institutions. It is composed of 15 judges and has its seat in The Hague, the Netherlands.
The 1982 United Nations Convention on the Law of the Sea (UNCLOS), known as the Montego Bay Convention, governs the rights and responsibilities of states with respect to the use of oceans and their resources. It provides for the delimitation of maritime spaces (territorial waters, EEZ, continental shelf, high seas) and freedom of navigation (right of “innocent passage”). One of the ICJ’s core tasks is to resolve disputes over the delimitation of maritime spaces, including EEZs. An EEZ is a strip of sea or ocean on which one riparian state (sometimes several states in the case of shared management agreements) has exclusive exploitation rights. This band extends up to 200 international nautical miles (370 km / 230 mi) from the baseline (coast), in the absence of other shorelines.
Maritime borders play a fundamental role in international relations. They directly influence a multitude of geopolitical, economic, legal and environmental fields. These boundaries define the areas over which states exercise sovereignty. Regarding national security, states want to protect their maritime spaces from foreign incursions, especially strategic areas (straits, access to ports, sea routes). With regard to natural resources, international law determines the rights of exploitation of these mineral, fossil and fishery resources. Thus, in view of the various issues, maritime borders are the subject of many international disputes. To ensure a peaceful settlement of these differences, international institutions such as the ICJ, the PCA and the ITDM play a key role in resolving conflicts.
ICJ maritime boundary cases
The delimitation of maritime boundaries and the resolution of disputes arising from them are based on different legal principles. The principle of equidistance is a key principle in maritime law. This is a method used to delimitate maritime boundaries by establishing a median line between two adjacent, adjacent or opposite coasts. A line that is nothing other than “the line whose points are equidistant from the nearest points to the baselines” (Article 7 of UNCLOS). This principle is based on the idea that the line delimiting the maritime spaces between two states must be drawn so as to be equidistant from each state, unless special circumstances justify a deviation.
The principle of equity is often applied in addition to the principle of equidistance. It aims to avoid arbitrary or unfair results, especially when the strict application of the rules of law could lead to imbalances or inequalities. It is for the judge to make his decision in the light of the case and to choose the method which he considers most appropriate for the fair delimitation of maritime spaces between the States concerned. The judge may decide to take into consideration geographical, geo-morphological and geological, bio-geographic and environmental, historical, economic and cultural, geopolitical and conduct-related factors. Geographical factors (shape of coasts, islands and reefs, distance between coasts, etc.) are by far the most important.
Islands are geographical features that may affect the delineation of maritime boundaries. They allow the state that owns them to expand its EEZ and potentially its continental shelf. For these reasons, in many current delimitation disputes, the islands are at the centre of the dispute. It is essential to know what international law means by “island”. To be qualified as an island, an island formation must meet two conditions: it must be a “natural land” and it must be “discovered at high tide”. Rocks that do not meet these two conditions and are not suitable for human habitation or a clean economic life do not have an exclusive economic zone or continental shelf.
In 2007, in its case of Nicaragua v. Honduras, the ICJ had to decide a maritime dispute concerning the two countries and the delimitation of their common maritime borders. The latter claimed sovereignty over 4 islands in the Caribbean Sea: Bobel Cay, Savanna Cay, Port Royal Cay and South Cay. The Court finally ruled in favor of Honduras on 8 October 2007, drawing a maritime delimitation based on the principle of equidistance, while taking into account the particular circumstances. The judgment clarified the allocation of marine resources, such as fisheries and hydrocarbons, and established principles for managing EEZs. This decision also set a precedent for other maritime boundary disputes.
Maritime boundary disputes: impacts and challenges of ICJ decisions
When the ICJ makes a decision, it is binding on all parties involved. Article 94 of the UN Charter states that “each Member of the United Nations undertakes to comply with the decision of the International Court of Justice in any case to which it is a party”. However, the ICJ does not have direct enforcement powers to enforce its decisions. It has no military force or sanctions mechanisms to coerce states. The ICJ is therefore dependent on the cooperation of these states and their political will to comply with the international legal standards it establishes. A state whose implementation of a decision is detrimental to its interests or geopolitical ambitions may seek to avoid it at all costs. Enforcement of ICJ decisions may be delayed by the need for the parties to negotiate a practical agreement to implement the terms of the judgment, or otherwise. This may include, for example, an agreement on the establishment of common fishing zones. The procedural delays are relatively long and span several years.
The role of the ICJ in resolving disputes relating to maritime borders may be limited by recourse to the International Tribunal for the Law of the Sea (ITDM). The ITDM is an independent international judicial body established by UNCLOS to ensure its compliance. 168 states are part of it. The tribunal is made up of 5 chambers specialized in maritime matters including the Chamber for the settlement of disputes relating to marine delimitation, relating to the seabed, relating to fisheries and relating to the marine environment. The TIDM has a dual competence: litigation and advisory. It shall adjudicate disputes relating to the application and interpretation of UNCLOS after being seized by a State or an international organization. The Seabed Dispute Settlement Chamber is competent to issue advisory opinions at the request of the Assembly or the Council of the International Seabed Authority. The Tribunal’s advisory jurisdiction extends to legal matters covered by an international agreement relating to the purposes of the Convention. Like the ICJ, the ITMD is specialized in the law of the sea and its procedures are faster. In addition, the Tribunal may order interim measures to protect the rights of parties pending a final decision, which is particularly useful in cases of maritime disputes.
States may also use international arbitration. It is a dispute resolution process, which consists of giving an arbitrator jurisdiction to settle a dispute rather than going through a court proceeding. It is based on the consent of the parties to a dispute. The arbitrators appointed shall render an arbitration award which shall have the relative authority of res judicata. The parties to the dispute must apply it in good faith. This practice remains limited.
In conclusion, the disputes over maritime boundaries, particularly in the South China Sea, highlight the geopolitical and economic issues associated with the delimitation of maritime zones. The ICJ, through its decisions, plays a central role in resolving these disputes by relying on legal principles such as equidistance and equity. However, the implementation of its judgments still faces major challenges, including a lack of coercive power. Complementary mechanisms such as ITDM or international arbitration can provide faster and more specialized solutions to maritime disputes. Ultimately, the resolution of these disputes depends not only on the application of international law but also on the cooperation of the States concerned, their political will and the search for practical arrangements to ensure peaceful and equitable management of marine resources.
