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US President Donald Trump accused the United Kingdom of “stupidity” over its plan to hand over ownership of the Chagos Islands, including the US air base on Diego Garcia, to Mauritius.

He cited the move as another reason for Washington to seize control of Greenland.

What are the Chagos Islands?

The Chagos Islands make up an archipelago in the center of the Indian Ocean. The UK took over the islands along with Mauritius in 1814 under the Treaty of Paris after the defeat of Napoleon.

In 1965, a Cold War agreement between the US and UK split the Chagos Islands from Mauritius, keeping control of the archipelago and renaming it as the British Indian Ocean Territory.

Over time, many Chagossians were removed from the island to create space for a military base, with most resettling in Mauritius. Although Mauritius gained independence in 1968, the Chagos Islands remain under British control.

Hoping to stave off Soviet military influence in the region, the US and UK built a major base on Diego Garcia in 1971. One of America’s most important — and secretive — overseas assets, Diego Garcia has helped launch two invasions of Iraq, served as a vital landing spot for bombers that fly missions across Asia, and has been linked to US rendition efforts.

Why is the UK relinquishing control of the islands?

Mauritius has for decades claimed sovereignty over the islands and pursued the case through international courts. In 2019, the International Court of Justice — the United Nations’ highest court — ruled that the UK must return the Chagos Islands to Mauritius “as rapidly as possible.” In its ruling, the court said the move would enable Mauritius to “complete the decolonization of its territory in a manner consistent with the right of peoples to self-determination.”

Although the judgment was non-binding, the UK has faced growing international pressure to give up control of the islands. Successive British governments — both Conservative and Labour — have argued it is a test of the UK’s commitment to international law.

Read more about the Chagos Islands in our full explainer.