Chagos Archipelago sovereignty dispute

Sovereignty over the Chagos Archipelago was disputed between Mauritius and the United Kingdom. Mauritius has repeatedly claimed the Chagos Archipelago as part of its territory and that the British claim is a violation of United Nations resolutions banning the dismemberment of colonial territories before independence. Given the absence of any progress with the UK, Mauritius took up the matter at various legal and political forums.

Between 1967 and 1973, the entire population of the Chagos Archipelago was either prevented from returning or forcibly removed by the United Kingdom. The main forcible removal of Diego Garcia’s population took place in July and September 1971.^[1] On 18 March 2015, the Permanent Court of Arbitration unanimously held that the marine protected area (MPA) which the United Kingdom declared around the Chagos Archipelago in April 2010 was created in violation of international law. The UK had argued that those undertakings were not binding and had no status in international law.^[2]

In 22 June 2017, by a margin of 94 to 15 countries, the UN General Assembly asked the International Court of Justice (ICJ) to give an advisory opinion on the separation of the Chagos Archipelago from Mauritius before the country's independence in the 1960s. In September 2018, the International Court of Justice began hearings on the case. 17 countries argued in favour of Mauritius.^[3][4] The UK and its allies argued that this matter should not be decided by the court but should be resolved through bilateral negotiations. On 25 February 2019, the judges of the International Court of Justice by thirteen votes to one stated that the United Kingdom is under an obligation to bring to an end its administration of the Chagos Archipelago as rapidly as possible. Only the American judge, Joan Donoghue, voted in favor of the UK. The president of the court, Abdulqawi Ahmed Yusuf, said the detachment of the Chagos Archipelago in 1965 from Mauritius had not been based on a "free and genuine expression of the people concerned." "This continued administration constitutes a wrongful act," he said, adding "The UK has an obligation to bring to an end its administration of the Chagos Archipelago as rapidly as possible and that all member states must co-operate with the United Nations to complete the decolonization of Mauritius."^[5]

On 3 November 2022, it was announced that the United Kingdom and Mauritius had decided to begin negotiations on sovereignty over the British Indian Ocean Territory, taking into account the recent international legal proceedings.^[6] On 3 October 2024, the UK agreed to hand over the Chagos Islands to Mauritius, although this was controversial given the presence of a U.S. military base on one of the islands.^[7] The United States endorsed the agreement^[8] though it can potentially harm its strategic interests.^[9] In geopolitical context, this settlement is expected to benefit India which is already maintaining a high presence in the area in close cooperation with Mauritius,^[10] while India is undertaking military cooperation with the U.S. as it finds ways to deal with the rising footprints of China in the Indian Ocean.^[11] On 22 May 2025, the agreement was signed by the UK and Mauritius; the dispute will end once the deal is ratified by both parties.^[12]