The International Court of Justice in The Hague ruled last week that the United Kingdom must cede control over the Chagos Islands, an Indian Ocean archipelago that was separated from Mauritius several years before Mauritius gained independence in 1968. The 13-1 verdict, while nonbinding, was an embarrassing defeat for the U.K. and a victory for many Chagossians who have sought to return to their homeland since being expelled in the 1960s and 1970s to make way for a U.S. military base on the island of Diego Garcia. In an interview with WPR, Marko Milanovic, a professor of public international law at the University of Nottingham in the U.K., discusses the many questions the ICJ’s ruling raises.

 Question: What prompted this case to be heard at the ICJ, and on what basis did the judges rule in Mauritius’ favor?The
ICJ can hear two types of cases. In contentious cases, it decides
disputes between states that have consented to its jurisdiction, and its
judgments are binding on the parties. In advisory cases, it is asked by
a competent U.N. body to give its opinion on a matter of international
law. The Chagos Islands case was an advisory one, in which the U.N.
General Assembly issued a request for an advisory opinion. This required
a lot of lobbying by Mauritius in order to persuade enough states to
vote in favor of its proposal for a request. In the end, the General
Assembly issued the request with 94 countries in favor, 15 against and
64 abstaining. On one hand, this result was a consequence of the U.K.’s
diminished standing on the international stage, especially after the
2016 Brexit referendum. On the other hand, it is also a consequence of
just how poorly, and inexcusably, the U.K. has treated the Chagossians,
thousands of whom were forcibly removed from the islands in the 1960s
and 1970s to make way for the Diego Garcia naval base. 

The General Assembly asked the ICJ to answer two questions. First, whether the decolonization of Mauritius, which included the separation of the Chagos Islands from Mauritius, was completed lawfully. Second, if it was not, the ICJ was asked to determine the consequences of the U.K.’s continued administration of the islands. The U.K. lost badly on both counts. On the first question, the court found that the British government carved out the Chagos archipelago in violation of Mauritius’ right to self-determination. On the second, the court held that the British administration of the islands was a continuing wrongful act, and that the U.K. was under an obligation to surrender control of the islands as soon as practicable.

Question:  Is the U.K. expected to abide by the court’s ruling? If not, what further recourse is available to Mauritius?

This is difficult to say. Formally speaking, the court’s opinion was only advisory in character, and the U.K. is under no legal obligation to comply with it as such. However, the opinion is an authoritative statement of the legal and factual situation regarding the status of the Chagos Islands, applying legal rules that are binding on the U.K. This is a common situation in international law—an institution’s decisions might not be binding, but they are nonetheless regarded as highly authoritative as they interpret and clarify binding legal rules. This is frequently the position of the U.N. General Assembly, for example when it pronounced Russia’s annexation of Crimea to have been unlawful. In the Chagos dispute, London may well argue that the ICJ was wrong, but after this ruling, few other states will be inclined to agree. 

What remains to be seen is just how much pressure the U.K. is subjected to, both internally and externally, to comply with the court’s opinion. Mauritius and like-minded states will, for example, use the opinion within the U.N. to criticize the U.K.’s reticence to return the islands to Mauritius. As with a lot of international law enforcement, the U.K.’s incentives to abide by the ruling are ultimately a function of the reputational cost incurred as a result of its noncompliance.

Question: What are the potential implications of this decision for the U.S. military base on Diego Garcia?
Officials in Mauritius have expressly said that they do not want the U.S. to abandon the Diego Garcia base—partly for economic reasons and partly because Mauritius does not want to antagonize the U.S. Mauritius believes, with some justification, that the likelihood of getting the Chagos Islands back depends on the intensity of U.S. opposition, which it wants to defuse by saying it does not wish to dismantle the base. In the event that the U.K. returns the Chagos Islands to Mauritius in the near future, the most likely outcome is that the U.S. will maintain its naval presence in Diego Garcia, but that it will have to negotiate the conditions with Mauritius rather than with the U.K. Mauritius would probably be accommodative in such talks.
The bigger issue is what will happen to the displaced Chagossians. They are the real victims here, and have been treated callously by almost all those concerned, especially by the British government. The current British government is of course almost entirely obsessed with Brexit, and has not said anything concrete yet on any possible negotiations with Mauritius or a change in policy regarding the return of displaced people to the Chagos Islands. The question is whether the return of any segment of the displaced population is really going to happen, and how. Even if all goes well in this regard—which is not at all a given, and Mauritius also needs to be held to account to safeguard the interests of Chagossians—this will likely not substantially affect the Diego Garcia naval base. U.S. armed forces are perfectly capable of operating military bases, even in highly populated areas, without compromising operations and security.