Diego Garcia is the largest island of the Chagos Archipelago, part of the British Indian Ocean Territory (BIOT). It has been used as a joint UK–U.S. military base since the 1970s, following the expulsion of the Chagossians by the UK government. The Chagos Islands have been a British overseas territory, but in early October 2024, the UK agreed to transfer sovereignty of the islands to Mauritius, while allowing the military base to remain under a 99-year lease, pending a treaty ratification.