The United Nations' highest court is set to deliver an advisory opinion on the legality of British sovereignty over the Chagos Islands in the Indian Ocean, the largest of which houses a strategically important U.S. military base.

Mauritius argues that the Chagos archipelago was part of its territory since at least the 18th century and was taken unlawfully by the United Kingdom in 1965, three years before Mauritius gained independence. Britain insists it has sovereignty over the archipelago, which it calls the British Indian Ocean Territory

Britain evicted about 2,000 people from the Chagos archipelago in the 1960s and 1970s so the U.S. military could build an air base on Diego Garcia. Many resettled in the U.K. and have fought in British courts to return to the islands.

Monday's opinion by the International Court of Justice is nonbinding.