The International Court of Justice has just heard four days of arguments as it weighs the legality of a hugely contentious colonial act: the UK’s decision to separate the Chagos Archipelago from Mauritius prior to the latter’s independence in 1968. Mauritius has been pursuing this case for decades, and has made substantial progress in recent years. And by claiming that the UK breached that right during the decolonisation process, it has forced important issues about self-determination up on the international agenda.

Britain detached the Chagos Islands from Mauritius in 1965, three years before Mauritian independence. From 1967 to 1973, some 1,500 Chagos islanders were gradually forced to leave their homes so that the largest island, Diego Garcia, could be leased to the US for a strategic airbase. Today, Diego Garcia hosts a major US military base and is a strategic node in US bombing campaigns in Afghanistan and Iraq. There are also reports it was used as a site for the CIA’s War on Terror-era rendition and interrogation programme, although the precise details are still opaque.

In the five decades since their removal, the islanders have fought for their right to return. In 2016, after several judicial challenges, Britain extended Diego Garcia’s lease until 2036 and declared that the expelled islanders would not be allowed to go back. In 2017, Mauritius successfully petitioned the United Nations to seek an ICJ advisory opinion on the legality of the separation. Coming just months after the Brexit referendum, the vote on whether to refer the matter to the ICJ was a humiliating diplomatic blow to Britain, which failed to rally support from fellow European states.

The referral was highly controversial. Under Article 96 of the UN Charter, the General Assembly can request that the ICJ give an advisory opinion on “any legal question”, but the UK argues that it’s inappropriate for the ICJ’s advisory opinion procedure to be used to intervene in a dispute between states that have not both consented to ICJ jurisdiction.

And while ICJ advisory opinions are not binding, the ramifications of the opinion will be highly significant; an opinion in favour of Mauritius may strengthen their position in any future negotiations, as well as putting significant international pressure on the UK over the status of the territory.

But what could be particularly critical is the decision’s impact on far broader issues of post-colonial sovereignty, and the legitimacy of colonial era independence arrangements.

Old wounds

The crux of the Mauritian claim is the right of self-determination. In its submission to the court, the Mauritian government claimed that the separation of the islands from Mauritius was in clear breach of UN resolution 1514, also known as the Colonial Declaration. Passed in 1960, it enshrined the right of self-determination for colonial peoples and specifically banned the breakup of colonies prior to independence. This was intended to keep borders stable, and to prevent colonial powers from simply absorbing colonial territory into their overseas territory so as to retain their sovereignty.

Yet in spite of this resolution, a number of states (including France and the UK) kept possession of parts of their former colonies following the decolonisation process.

In his opening submission, Sir Anerood Jugnauth, Mauritius’s defence minister, alleged that his country was coerced into giving up the islands, resulting in “the unlawful detachment of an integral part of our territory on the eve of our independence”. A number of classified documents made public on Wikileaks were used as key evidence of the diplomatic pressure Britain exerted over the decision to separate the islands. “The choice we were faced with was no choice at all: it was independence with detachment [of the Chagos archipelago] or no independence with detachment anyway,” Jugnauth told the court.

For his part, the UK’s solicitor general, Robert Buckland, stated that while the UK accepted that the removal of the Chagossians and their treatment thereafter “was shameful and wrong” it had already been resolved in a 1982 agreement on compensation. The UK also contended that the right to self-determination was not established in international law until the 1970s, after the separation of the islands from Mauritius.

Global implications

But for all that the UK might want to see this case viewed as narrowly as possible, it is inevitably part of something greater. Around the world, many territories remain under the administrative or sovereign control of several states. What the Chagos case indicates is that there is now serious momentum behind efforts to review and challenge their status, and that a question mark now hangs over a number of colonial era territorial arrangements.

22 interested parties, among them the African Union and many former colonies, have taken part in the Chagos hearings. Speaking of their decision to participate in the proceedings, representatives for South Africa referred to the duty of all member states of the UN “to assist the general assembly to remove the last vestiges of colonialism”. As Professor Philippe Sands QC, representing Mauritius, told the ICJ: “The right to self-determination is not a ‘heritage’ issue. This is not Africa in the late 19th or early 20th century. This is September 2018.”

Miriam Bak McKenna, Postdoctoral Fellow in International Law, Lund University.

This article first appeared on The Conversation.