UK Cedes Chagos Islands to Mauritius
Written by Nestor Lim
In a rare act of what some considered as magnanimity in diplomacy, the United Kingdom has agreed to cede sovereignty of the Chagos Island Group to Mauritius following the non binding advisory opinion of the International Court of Justice (ICJ) that states that the UK has an obligation under international law to end its administration over said property.
The Island Group are located in the Indian Ocean and is under the rule and administration of the British Crown. The Republic of Mauritius has a claim over said islands since historically, during the time that they were a French colony, said islands are their dependency. However, France ceded the Republic and its dependencies to the UK through the Treaty of Paris of 1814. When Mauritius got their independence from UK, they sought to include the Chagos Island Group as part of their territory.
Under public international law, a Sovereign State can legally acquire or lose part of its territory through the method called cession where one State cedes its dominion over a property to another State either voluntarily or involuntarily. This is normally formalized through a treaty signed by the relinquishing and the accepting States.
The UK and Mauritius have both agreed to formalized this situation by signing a treaty following international norms. At first glance, it would seem that both the UK and Mauritius are going through the expected steps needed for cession of territory to happen under customary international law. However, there are varying opinion as to whether there is actually cession of territory in this case. Considering that the Chagos Islands has always been part of Mauritius' territory, as claimed by some, then the UK never exercised sovereign dominium over said islands and thus, there is no cession to speak as far as the "return" of these Islands is concerned. In fact, the advisory opinion of the ICJ considers the detachment of the Chagos Islands as illegal and therefore there is no cession of territory, at least in the context of decolonizing non self-governing territory.
Despite the advisory opinion of the ICJ on the legality of the detachment of Chagos Islands, the fact that the UK has exercised de facto sovereignty over the islands make one conclude that cession has indeed taken place. In international law, cession that is illegal does not necessarily mean that it is invalid, unless certain conditions are met (e.g., the reason of the cession is against jus cogens).
The subsequent developments in this area would shed more light on the propriety of calling the situation a cession of territory. How the treaty between UK and Mauritius is worded as well as the reaction and opinion of other sovereign states and pundits would be helpful. In any case, it would be an interesting case study for students of public international law.
Read the advisory opinion of the ICJ here: https://www.icj-cij.org/sites/default/files/case-related/169/169-20190225-ADV-01-00-EN.pdf
