Zanzibar was a British protectorate from 1890 until its independence in 1963. Unlike a colony, a protectorate retained a local ruler—in this case, the Sultan of Zanzibar—while Britain controlled or influenced external affairs and exercised substantial political power.
Britain declared the protectorate in 1890 after negotiating with the Sultanate and European powers over control of East African territories. Zanzibar's location off the coast of present-day Tanzania made it a major commercial centre linking Africa, Arabia, India, and the wider Indian Ocean. It was also historically associated with the clove trade and the regional slave trade, which Britain pressured the sultanate to suppress.
The protectorate ended on December 10, 1963, when Zanzibar became an independent constitutional monarchy within the Commonwealth. The arrangement was short-lived: the Zanzibar Revolution in January 1964 overthrew the sultan, and in April 1964 Zanzibar united with Tanganyika. That union formed the country now known as Tanzania.