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The Chagos Archipelago
Indian Ocean atolls administered by Britain, claimed by Mauritius and the Maldives
In the middle of the Indian Ocean, about 500 kilometers south of the Maldives, the Chagos Archipelago is a scatter of low coral atolls, and at its southern edge lies Diego Garcia, home to a joint UK–US military base. The United Kingdom has administered the islands since 1965 as the British Indian Ocean Territory. Mauritius claims them, a position backed by a 2019 ICJ advisory opinion and a UN General Assembly resolution. In May 2025 the two governments signed a treaty transferring sovereignty to Mauritius while keeping Diego Garcia under UK control for an initial 99 years. As of October 2026, that treaty has not entered into force, and the Maldives has challenged the transfer.
The archipelago comprises seven atolls and some 60 islands with a total land area of about 56 square kilometers, scattered across the Great Chagos Bank, the largest atoll structure in the world. Diego Garcia, a V-shaped atoll enclosing a deep lagoon, accounts for about half the land and holds the runway, harbor, and support facilities of the base, where a few thousand military personnel and contractors live. There is no permanent civilian population. The outer atolls, including Peros Banhos and Salomon, are uninhabited and lie within a large marine protected area that the UK declared in 2010, which an international tribunal later found had been created without proper regard for Mauritius's rights. Mauritius lies more than 2,000 kilometers to the southwest.
Britain detached the archipelago from colonial Mauritius in 1965, three years before Mauritian independence, and between 1968 and 1973 removed an estimated 1,400 to 1,700 Chagossians to make way for the US base. Mauritius has pressed its claim ever since. In 2019 the International Court of Justice advised that the separation was unlawful and that UK administration should end, and the General Assembly endorsed that view. The treaty signed on May 22, 2025, would give Mauritius sovereignty and the UK rights over Diego Garcia, but its implementing bill lapsed when the UK parliamentary session ended in April 2026, amid objections from Washington, and talks among the three governments continue. The Maldives, which calls the islands Foalhavahi, now asserts a claim of its own, and Mauritius cut diplomatic ties with it in early 2026. Chagossians remain divided over the outcome.