How did Mauritius's claim to the Chagos Archipelago develop?

The Chagos Archipelago was historically administered as a dependency of Mauritius under French and later British rule. In 1965, the United Kingdom detached the archipelago from the Mauritius colony to form the British Indian Ocean Territory, a move Mauritius later argued was a forced condition for its 1968 independence.12

Following the forced removal of the native Ilois population to facilitate a U.S.-U.K. military base on Diego Garcia, the sovereignty dispute intensified. In 2017, the UN General Assembly requested an advisory opinion from the International Court of Justice (ICJ) regarding the legality of this decolonization. The 2019 ICJ ruling concluded that the process was illegal and recommended that the United Kingdom end its administration.12

These developments led to a diplomatic shift, culminating in a tentative agreement in 2024 and the signing of a final treaty in May 2025 to transfer sovereignty of the archipelago to Mauritius, pending final legislative approval.2