The Zanzibar Archipelago, now part of the Southeast African republic of Tanzania, is a group of islands lying in the Indian Ocean off the coast of Tanganyika. It comprises the main southern island of Unguja (also known as Zanzibar), the smaller northern island of Pemba, and numerous surrounding islets. With a long history of Arab rule dating back to 1698, Zanzibar was an overseas territory of Oman until it achieved independence in 1858 under its own Sultanate. In 1890 during Ali ibn Sa'id's reign, Zanzibar became a British protectorate, and although never formally under direct rule was considered part of the British Empire.