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Expanded History

History of British Indian Ocean Territory

From antiquity to the modern era — the historical eras, key events, and narrative that shaped British Indian Ocean Territory.

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Overview

The British Indian Ocean Territory (BIOT) covers 54,400 km2 of ocean, including the reefs and islands of the Chagos Archipelago. The islands within the territory cover a total of around 60 km2, and lie between 4 and 8°S and 70 and 75°E. The total area of near-surface coral reefs is some 4,000 km2, which is approximately 1.5% of the total global area of reefs, a very major proportion of an important and increasingly threatened global heritage. The nearest neighbouring islands and reefs are those of the Maldives, with the southernmost atoll, Addu, being some 500 km to the north, separated by a channel some 2,200–3,300 m deep. The nearest continental land-area is that of Sri Lanka, which is over 1,500 km distant. To the west, the Seychelles lie over 1,800 km away, and the mainland coast of East Africa some 3,400 km distant. The Andaman and Nicobar Islands, the coast of Sumatra and Cocos Keeling Islands lie approximately 3,500 km to the east. The islands and reefs form the southernmost part of a long shallow ocean ridge, the Laccadives–Chagos Ridge, which runs almost directly north–south. The Archipelago consists of a variety of reefs with their associated low-lying coralline islands. There are five atolls: Chagos Bank, Peros Banhos, Salomon, Egmont and Diego Garcia; and ten reefs and submerged shoals including Blenheim Reef, Speakers Bank, Pitt Bank and Centurian Bank.

BIOT was established by an Order in Council on 8 November 1965, having been a British territory since 1814, but formerly administered as a dependency of Mauritius. At present, land use is for military purposes only. There are licensed fisheries, notably for offshore tuna fishing, and a licensed reef fishery operated by Mauritian fishermen who visit the reefs for a few months each year (BIOT Administration 1997).

Historical Eras

The major periods of {country}’s history at a glance.

  1. Uninhabited Prehistory

    The Chagos Archipelago remained uninhabited throughout recorded history prior to European colonization, with no indigenous population ever documented. The remote coral atolls, lying over 1,500 km from the nearest continental landmass, were known to Arab and South Asian mariners but never permanently settled. European explorers charted the islands from the sixteenth century onward.

  2. French Colonial Period

    1783 – 1814

    France claimed the Chagos Archipelago as a dependency of Mauritius (then Île de France) in the late eighteenth century, establishing coconut plantations worked by enslaved Africans. The islands, particularly Diego Garcia, served as a provisioning stop for vessels traversing the Indian Ocean. This era introduced the first permanent human habitation of the archipelago.

  3. British Dependency Era

    1814 – 1965

    Britain acquired the Chagos Archipelago through the Treaty of Paris (1814) following the Napoleonic Wars, administering it as a dependency of Mauritius and later the Seychelles. Copra plantations continued to operate, sustaining a settled Chagossian community of several hundred people known as the Ilois. The islands remained an obscure imperial backwater until strategic considerations during the Cold War prompted a fundamental reassessment of their value.

  4. BIOT Establishment

    1965 – 1973

    The British Indian Ocean Territory was formally created by Order in Council on 8 November 1965, detached from Mauritius and the Seychelles ahead of their respective independences. A secret agreement with the United States provided for the construction of a major joint military facility on Diego Garcia. Between 1967 and 1973, the entire Chagossian population was forcibly relocated, primarily to Mauritius, in one of the most controversial acts of British colonial administration in the postwar period.

  5. Military Territory & Legal Disputes

    1973 – present

    Diego Garcia became a strategically critical joint UK-US naval and air support facility, used extensively during the Gulf War, the War in Afghanistan, and operations in Iraq. In 2000, the British High Court ruled that the expulsion of the Chagossians had been unlawful, though subsequent government Orders in Council again restricted resettlement, triggering prolonged legal battles. In 2024, the UK and Mauritius reached a landmark agreement in principle to transfer sovereignty of the archipelago to Mauritius, placing the territory's future status in question.

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