The International Court of Justice is a principal judicial organ of the United Nations, established by the United Nations Charter in June 1945. It has jurisdiction to settle, in accordance with international law, legal disputes submitted to it by States and to give advisory opinions on legal questions referred to it by duly authorized United Nations organs. Although the ICJ's opinions are not binding, they carry great weight under international law.

In June 2017, the UN General Assembly adopted resolution 71/292 (A/71/L.73) entitled “Request for an advisory opinion of the International Court of Justice on the legal consequences of the separation of the Chagos Archipelago from Mauritius in 1965”. In particular, the ICJ was requested to render an advisory opinion on the following questions: a) Was the process of decolonization of Mauritius lawfully completed when Mauritius was granted independence in 1968, following the separation of the Chagos Archipelago from Mauritius, b) What are the consequences under international law arising from the continued administration by the UK of the Chagos Archipelago, including with respect to the inability of Mauritius to implement a programme for the resettlement on the Chagos Archipelago of its nationals?

The United Kingdom gained control of Mauritius, including the Chagos Archipelago in 1814. In 1965 the United Kingdom detached the Chagos Archipelago from the colony of Mauritius and a British colony became independent three years later. In 1966 the UK leased Diego Garcia, the largest of 60 small islands comprising the Chagos Archipelago, to the US. Afterwards, around 1,500 people were forced to remove the island due to the construction of the US airbase, - today, one of the largest US military bases in the world, and home to an estimated 4,000 troops. In 2016, the UK's foreign ministry extended Diego Garcia's lease until 2036, and declared the expelled islanders would not be allowed to go back.

In this context, Anerood Jugnauth, former Mauritian president, said: “More than 50 years after independence the process of decolonisation of Mauritius remains incomplete. This is a result of the unlawful detachment of an integral part of our territory on the eve of our independence", he told the judges.”

Mauritius’s government argues that the Separation of the Chagos Archipelago from Mauritius in 1965 was in breach of UN resolution 1514 “Declaration on the Granting of Independence to Colonial Countries and Peoples”. The UN resolution 1514, adopted in 1960, banned the breakup of colonies before independence. The UK argues that the legal question is essentially about a bilateral dispute between States that have not consented to ICJ jurisdiction over that dispute, and that it is inappropriate for the ICJ advisory opinion procedure to be used.

The International Court of Justice (ICJ) is going to deliver its Advisory Opinion in respect of the Legal Consequences of the Separation of the Chagos Archipelago from Mauritius in 1965 on Monday 25 February 2019.