Chagos Archipelago

The Chagos Archipelago (/ˈtʃɑːɡəs, -ɡoʊs/, also UK: /ˈtʃeɪɡɒs/) or Chagos Islands (formerly Bassas de Chagas, and later the Oil Islands) is a group of seven atolls comprising more than 60 islands in the Indian Ocean about 500 kilometres (310 mi) south of the Maldives archipelago. This chain of islands is the southernmost archipelago of the Chagos–Laccadive Ridge, a long submarine mountain range in the Indian Ocean. In its north are the Salomon Islands, Nelsons Island and Peros Banhos; towards its south-west are the Three Brothers, Eagle Islands, Egmont Islands and Danger Island; southeast of these is Diego Garcia, by far the largest island. All are low-lying atolls, save for a few extremely small instances, set around lagoons.

The islands were first permanently settled by Europeans. From 1715 to 1810, the Chagos Islands were part of France's Indian Ocean possessions, administered through Isle de France—which was a colony of France (later renamed as Mauritius). Under the Treaty of Paris in 1814, France ceded Isle de France and the Chagos Islands to the United Kingdom.

In 1965, the United Kingdom split its administration of the Chagos Archipelago away from Mauritius and into the British Indian Ocean Territory (BIOT), to allow the United States to build Naval Support Facility Diego Garcia, which operates under a special agreement allowing significant US military presence. The islands were formally established as an overseas territory of the United Kingdom on 8 November 1965.

The only permanent inhabitants are employees of the military, including civilian contracted personnel, on Diego Garcia. The Chagos Islands are the homeland of the Chagossians, a Bourbonnais Creole–speaking people, though since 1971 no Chagossians have been allowed to live there. The United Kingdom expelled the entire Chagossian population from the archipelago at the request of the United States between 1967 and 1973 The main forcible removal of Diego Garcia's population took place in July and September 1971. In 2026, a group of Chagossians returned to the archipelago without government permission in an effort to reestablish the settlement on Île du Coin, and began legal action to establish their right to stay permanently.

Mauritius engaged in a sovereignty dispute with the UK, claiming the Chagos Archipelago as part of Mauritius. The International Court of Justice (ICJ) in 2019 and the International Tribunal for the Law of the Sea (in 2021) both stated that the UK had an obligation to return the islands to Mauritius. In October 2024, the British government announced it would transfer the Chagos Islands to Mauritius subject to finalisation of a treaty. The transfer agreement was signed on 22 May 2025, with the provision that the island of Diego Garcia would be leased back to the UK for at least 99 years. The UK government expected the treaty to be ratified sometime in 2026. The UN Committee on the Elimination of Racial Discrimination has expressed "deep concern" at the terms of the deal. Opponents of the deal have cited Article 298 (b) of the United Nations Convention on the Law of the Sea (UNCLOS) as giving the British government an invokable legal exemption from "disputes concerning military activities, including military activities by government vessels and aircraft engaged in non-commercial service", and have argued that the British government's case was misleading.