Mauritius and the United Kingdom on Thursday signed an agreement officially transferring sovereignty over the Chagos Archipelago to Mauritius. However, under the terms of the deal, the United Kingdom and the United States will retain control of their joint military base on Diego Garcia for a period of 99 years, allowing both countries to maintain their strategic presence in the Indian Ocean.
The deal finalizes an arrangement tentatively reached last year, when the U.K. agreed to cede sovereignty of the archipelago while preserving its access to the Diego Garcia base. At the time, Foreign Secretary David Lammy hailed the agreement, saying it had “saved the base.”
The Chagos Archipelago, which includes Diego Garcia, was originally part of the British colony of Mauritius. However, in 1965—shortly before granting independence to Mauritius in 1968—the U.K. separated the archipelago and designated it as part of the new “British Indian Ocean Territory” setting the stage for a decades-long territorial dispute.
In 1966, the U.K. leased Diego Garcia to the United States, leading to the forced displacement of approximately 2,000 native Chagossians. The military installation has since become a key strategic asset for both Washington and London.
In 2019, the International Court of Justice (ICJ) issued a non-binding advisory opinion calling on the U.K. to return the archipelago to Mauritius. The ruling placed diplomatic pressure on London, prompting concern in Washington about potentially losing access to the Diego Garcia base. As a result, the U.S. encouraged the U.K. to reach an agreement with Port Louis that would allow them to comply with the ICJ's advisory while securing long-term military use of the base.
Diego Garcia has remained vital to U.S. military operations across the broader Middle East and Indo-Pacific. In March, the base made headlines after the U.S. deployed at least six B-2 stealth bombers and other aircraft there amid rising tensions with Iran. The move followed a letter sent by then-President Donald Trump to Iranian Supreme Leader Ali Khamenei, warning of possible military action unless Tehran met Washington’s demands concerning its nuclear program and foreign policy.
Given the ongoing rapprochement between Iran and Gulf Arab states, many analysts believe that a future U.S. strike on Iran—if it were to occur—would likely be launched from Diego Garcia rather than bases in the Gulf, as regional governments may be unwilling to support direct military operations from their soil. This reality has only heightened the strategic value of the base for both the U.S. and U.K.