Chagos Islands | Deal in deep water

In a social media post, U.S. President Donald Trump asked the U.K. to “not give away Diego Garcia”, referring to the site where a U.S.-U.K. military base is located in the Chagos archipelago.

The U.K. deal concerning the Chagos Island grouping is the result of a long negotiation surrounding the archipelago, located in the central Indian Ocean, around 1,600 km from the tip of the Indian subcontinent. The archipelago, positioned around 2,000 km north-east of Mauritius, about mid-way between East Africa and Indonesia, is an overseas territory of the U.K., one of 14 remaining in the post-colonial era.

Officially referred to as the British Indian Ocean Territory (BIOT), the grouping consists of 60 islands set in seven ring-shaped coral atolls. The largest of the lot, Diego Garcia, plays host to the joint U.S.-U.K. military base, which reportedly has an airfield, a deep-water port, and communications- and surveillance-related infrastructure. The islands have American and British military presence and contract civilian personnel but do not host a permanent civilian population as of today.

The islands were uninhabited when they were discovered by Portuguese explorers in the 16th century. Given its strategic location on international trade routes, several foreign powers sought to establish control over the archipelago. In the late 18th century, France took over the islands, along with Seychelles, treating them as dependencies of Mauritius. In the early 19th century, the islands were taken over by the U.K.; Mauritius and its dependencies were proclaimed colonies of Britain in 1814 under the Treaty of Paris. Seychelles was detached from Mauritius and became a separate colony in 1903. The BIOT came into being in 1965 following the U.S.-U.K. agreement.

Mauritius gained independence in 1968; the U.K. reportedly paid it a £3 million grant to maintain control over the Chagos Islands. In 1971, a military facility was constructed on Diego Garcia, and the local Ilois/Chagossians, descended from African slaves and Indian plantation workers, were offered the choice to relocate to Seychelles or Mauritius. While most resettled in Mauritius, a few moved to the U.K.

Right to return

In 2000, the British High Court found that the removal of the Chagossians was illegal and granted them the right to return. While this was upheld by the Court of Appeal in 2007, it was reversed by the House of Lords in 2008. An ICJ advisory ruling in 2019 found that the decolonisation process pertaining to Mauritius was illegal and recommended that the U.K. stop its administration of the Chagos Islands.

Although non-binding, the ruling had international weight, and the U.K. government began negotiations over this in 2022, under then-Conservative Prime Minister Rishi Sunak. An agreement was sketched out in October 2024. A final treaty to transfer sovereignty over the islands to Mauritius was signed in May 2025 by Labour Prime Minister Keir Starmer and Mauritius Prime Minister Navin Ramgoolam. Before the treaty enters into force, it needs to be ratified by legislation, and a draft law dealing with this is progressing through Parliament.

The plan, estimated to cost £3.4 billion, envisages the handing over of the Chagos Islands to Mauritius by the U.K. and the leasing back of the military base in Diego Garcia for 99 years at an average cost of £101 million a year. The deal includes a £40 million trust fund to support Chagossians, who will be permitted to resettle in all islands except Diego Garcia.

Mr. Trump has called the deal “an act of great stupidity”, and the potential loss of the land “a blight on our Great Ally”. Describing the island as “strategically located”, Mr. Trump indicated that Diego Garcia may be brought into play “in order to eradicate a potential attack by a highly unstable and dangerous Regime”— a reference to Iran. He has also linked the deal to his own designs to acquire Greenland.

The U.K. has maintained that the deal is vital for the U.K.’s security interests, with Mr. Starmer noting that the deal was required to avert the risk of a future binding legal judgment affecting the U.K.’s ability to use the Diego Garcia base. On the other hand, the deal has invited criticism from Conservatives and Reform UK, who view Mauritius’s ties with China with suspicion.