“Leased”
Between 1968 and 1973, the Chagossian (Îlois) inhabitants were forcibly expelled from Diego Garcia by the UK Government so that a joint US/UK military base could be established on the island.
Many were deported to Mauritius and the Seychelles, following which the United States built the large Naval Support Facility Diego Garcia, which has been in continuous operation since then.
In 2019, this action and continued British administration of the archipelago were deemed illegal by the International Court of Justice in The Hague, a ruling the United Nations General Assembly supported.
In 2023, Human Rights Watch condemned the action as a crime against humanity.In the interest of completeness both Great Britain and North America were also once uninhabited.
Also, originally Iceland was uninhabited. The Norse created a colony there of - as you put it - "people and slaves". That equivalent history surely does not affect the legal status of the descendants of those people now living in Iceland. Why should it affect the people now living in the BIOT?