The U.S.A. has had a Nava Base at Guantanamo Bay, Cuba since American occupation in 1898. Why they have a base there is detailed in the official
Gitmo website. Originally occupied by military invasion, the U.S.A. now occupies the naval base under a long term lease from the government of Cuba.
The reasons the Al Qaeda and Taliban
detainees are being kept there are several, including:
* it is a secure military facility under the unfettered control of the U.S.A. unlike the Kandahar air base, which is subject to the sovereignty of Afghanistan, where the U.S.A.'s occupation and conduct is subject to international law.
* although under American control, the naval base is not sovereign U.S.A. terrritory, so the detainees do not have the protection of American constitutional law, and the administration is free of any potential involvement of the other branch of government, the judiciary, with respect to the rights of any detainees.
Historically, the British had a similar detention island. You know the one.