Islands; in the early 20th century, they produced approximately 90% of the world's supply of cloves. Zanzibar was also a major transit point in the African Great Lakes and Indian Ocean slave trade. Zanzibar attracted ships from as far away as the United States, which established a consulate in 1833. The United Kingdom's early interest in Zanzibar was motivated by both commerce and the determination to end the slave trade. In 1822, the British signed the first of a series of treaties with Sultan Said to curb this trade, but not until 1876 was the sale of slaves finally prohibited. The Heligoland-Zanzibar Treaty of 1890 made Zanzibar and Pemba a British protectorate, and the Caprivi Strip in Namibia became a German protectorate. British rule through a Sultan remained largely unchanged from the late 19th century until 1957, when elections were held for a largely advisory Legislative Council. Independence and Union of Tanganyika and Zanzibar In 1954, Julius Nyerere, a school teacher who was then one of only two Tanganyikans educated to university level, organized a political party—the Tanganyika African National Union (TANU). On 9 December 1961, Tanganyika became independent, though retaining the British monarch as Queen of Tanganyika, and Nyerere became Prime Minister, under a new constitution. On 9 December 1962, a republican constitution was implemented with Mwalimu Julius Kambarage Nyerere as Tanganyika's first president. Zanzibar received its independence from the United Kingdom on 10 December 1963, as a constitutional monarchy under its Sultan. On 12 January 1964, the African majority revolted against the sultan and a new government was formed with the ASP leader, Abeid Karume, as President of Zanzibar and Chairman of the Revolutionary Council. In the first few days of what would come to be known as the Zanzibar Revolution, between 5,000 and 15,000 Arabs and Indians were murdered. During a series of riots, followers of the radical John Okello carried out thousands of rapes and destroyed homes and other property. Within a few weeks, a fifth of the population had died or fled. It was at this time that the Tanganyika army revolted and Britain was asked by Julius Nyerere to send in troops. Royal Marines Commandos were sent by air from England via Nairobi and 40 Commando came ashore from the aircraft carrier HMS Bulwark. Several months were spent with Commandos touring the country disarming military outposts. When the successful operation ended, the Royal Marines