The Chagos Islands: Africa's Unfinished Decolonization

Mauritius became independent from Britain in 1968, but not all of it. Three years earlier, in 1965, the British government detached the Chagos Archipelago, a scattering of islands more than a thousand miles northeast of the Mauritian mainland, and kept it under direct British control as the newly created British Indian Ocean Territory. Between the late 1960s and early 1970s, Britain forcibly removed the archipelago’s entire population, roughly 1,500 to 2,000 Chagossians, to make way for a joint UK-US military base on the largest island, Diego Garcia, relocating most of them to Mauritius and the Seychelles with little compensation.

Mauritius never accepted the loss as final, and in 2017 the UN General Assembly asked the International Court of Justice to weigh in. The court’s advisory opinion, issued February 25, 2019, found that Mauritius’s decolonization “was not lawfully completed” when Britain carved off the Chagos Archipelago before granting independence, and that the UK was “under an obligation to bring to an end its administration of the Chagos Archipelago as rapidly as possible.” An advisory opinion carries no binding enforcement power on its own, so the General Assembly followed up on May 22, 2019, with a resolution formally welcoming the court’s findings and demanding that Britain “unconditionally withdraw its colonial administration” within six months. The vote was lopsided: 116 countries in favor, six against, including the UK and the United States, and 56 abstentions.

That six-month deadline expired on November 22, 2019, and Britain let it pass. For years afterward, UK officials continued to refer to the territory by its own name, the British Indian Ocean Territory, and rejected the General Assembly vote and the ICJ’s opinion as non-binding on London’s continued administration of the islands. The displaced population’s right of return remained unresolved throughout that period: the 2019 resolution had urged the UK to cooperate with Mauritius on resettling Mauritian nationals, Chagossians among them, in the archipelago, and no resettlement took place.

Britain held out for another five and a half years after that deadline passed. Negotiations with Mauritius eventually produced a treaty, signed on May 22, 2025, under which the UK would transfer sovereignty over the entire archipelago to Mauritius while retaining Diego Garcia itself on a 99-year lease, paying Mauritius roughly $136 million a year for the arrangement. The deal still required ratification, and that process stalled in the House of Lords after opposition lawmakers argued it could conflict with a separate 1966 UK-US agreement governing the joint military base, leaving the treaty signed but not yet in force well into 2026.