Complex sentence: The United Kingdom excised the Chagos Archipelago from Mauritian territory prior to Mauritian independence in 1965, and gradually depopulated its indigenous population and leased the biggest island Diego Garcia to the United States.
Split into simpler sentences: The United Kingdom excised the Chagos Archipelago from Mauritian territory prior to Mauritian independence in 1965. The UK gradually depopulated the archipelago's indigenous population and leased its biggest island, Diego Garcia, to the United States.