Approximate timeline of Chagos Islands sovereignity
This is based on the advisory opinion of the ICJ from 2019 and the Wiki article on Chagos Islands:
16th Century - Portuguese discovery: The Chagos Archipelago was first recorded by the Portuguese in 1512 during their voyages through the Indian Ocean. The islands were named "Bassas de Chagas" after the Holy Wounds of Christ (Wiki).
Early 18th Century - French control: The French began controlling the Chagos Archipelago when they settled in nearby Île Bourbon (now Réunion) in 1665 and Isle de France (now Mauritius) in 1715. Note that all three territories: Chagos Islands, Mauritius and Réunion were uninhabited by humans before Europeans arrived. Hence they weren't "colonized" in the traditional sense of the word.
1770s: the French issue for coconut plantations, and some of the islands, like Diego Garcia, began to be settled by French planters. The primary activity during this period was the production of coconut oil (Wiki).
1786 - British claim: The British formally claimed the Chagos Islands in 1786 but did not effectively control them until after the defeat of Napoleon.
1814 - Treaty of Paris: following the Treaty of Paris, France ceded Mauritius and its dependencies, including the Chagos Archipelago, to the British. The islands were governed as a dependency of British Mauritius (Wiki).
1793 onwards: The British established coconut plantations across the islands, including on Diego Garcia. The labor force for these plantations was comprised of enslaved people brought from Africa and India by the French. This population formed the core of what would later become the Chagossians (ICJ ruling, paragraph 113 and Wiki).
1830s: The enslaved workers were emancipated after Britain abolished slavery, but the Chagossians continued to work on the plantations under indentured conditions. (ICJ ruling, paragraph 113 ).
1903 - Administrative Separation: The Chagos Archipelago was administratively separated from the Seychelles and attached to British Mauritius, aligning its governance more closely with the broader colonial structure of the Indian Ocean (Wiki).
1965 - the "Lancaster House agreement" is signed between Mauritius and the UK, confirming the temporary detachment of the Chagos Archipelago from Mauritius. The UK paid out £3 million in compensation and agreed to return the islands "if the need for the facilities on the islands disappeared" (ICJ ruling, paragraph 108).
Between 1967 and 1973, the entire population of the Chagos Archipelago was either prevented from returning or forcibly removed and prevented from returning by the United Kingdom. The main forcible removal of Diego Garcia’s population took place in July and September 1971. (ICJ ruling, paragraph 43).
Once again note that prior to 1965 neither Mauritius nor the Chagos Islands were ever independently controlled by anyone other than Europeans. If coconut plantations weren't allowed to use slaves, there would be no
Opinion of the ICJ
According to the 2019 ICJ ruling, the 1965 Lancaster House agreement might be considered invalid for the following reasons:
Lack of genuine consent: Mauritius was still a colony under the authority of the United Kingdom when the agreement was made. The representatives of Mauritius (supposedly) did not have full ability to exercise independent legislative or executive powers. Therefore its suspected that the agreement was not based on the free and genuine expression of the will of the people of Mauritius (Paragraphs 98-112).
Violation of international law: The detachment of the Chagos Archipelago violated the territorial integrity of Mauritius, which was a non-self-governing territory. This contravened international law principles enshrined in the UN Charter and the right to self-determination (Paragraphs 140-162).
Incomplete decolonization: The detachment of the Chagos Archipelago meant that the process of decolonization for Mauritius was not lawfully completed when it became independent in 1968 (Paragraphs 170-174)
Obligations of the administering power: The UK, as the administering power, had an obligation to respect the territorial integrity of Mauritius, which included the Chagos Archipelago. The agreement disregarded this requirement (Paragraphs 144-169).
The elephant in the room
The ICJ dedicated a grand total of one paragraph (113) to the history of the "Chagossian" people and never discusses the fact that:
- Europeans have discovered the islands first, including Mauritius. Seriously, not a single mention of the full timeline is made in the entire 47-page document, despite this being of significant importance.
- The vast majority of non-European residents of the Chagos Islands and Mauritius were brought there by a European power who held a genuine sovereignty claim.
- The islands were forcibly assigned to Mauritius by the UK and thus even if the Chagossians are the "true" owners of the islands, it should theoretically become an independent property of the descendants of the "Chagossian" people rather than Mauritius itself.
The ICJ has made their decision; now let them enforce it
At the end of the day it hardly matters what the ICJ has ruled. It's up to Mauritius or a larger power to deploy enough troops to kick out the American military base and likewise prevent the British military from regaining control. It's possible that the UK will one day voluntarily relinquish their claim but given the (arguably) one-sided ICJ ruling and the full history of the islands, I wouldn't bet on this happening in the 21st century.