Diego Garcia is the largest island of the Chagos Archipelago. 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 is a British overseas territory, though a treaty to transfer sovereignty from the UK to Mauritius was signed on 22 May 2025, with a provision that the military base at the island would remain under British control for at least 99 years. The agreement may be renewed for an additional 40 years after the initial 99-year period, and for an additional period thereafter.