The suzerains of the empire had been traders for many centuries and used Zanzibar as their main port, originally for slaves and ivory. However, in 1812 it was discovered that cloves grew very well in the south of Zanzibar and the neighboring island of Pemba. The demand for cloves and other spices was high.
Sultan Seyyid Said of Oman saw the possibilities in this trade and began to invest in clove plantations starting in 1820. In order to maximize production of cloves, he used slaves from much of east and central Africa. Ultimately most of Africa between the East African coast and the Congo River basin, or an area of over 1 million square miles, was affected by the slave trade which persisted to the 1890s.
In order to gain cheap labor, the Omani Arabs, beginning with Seyyid Said, encouraged African tribes to turn on each other so as to provide slaves through prisoners of war. By the 1820s 8,000 slaves a year were brought to Zanzibar and Pemba.
This was opportune as the market for slaves was drying up because of pressure from Europe. (By 1873 before the British forced the end of the slave trade by sending a naval squadron, the number of slaves brought to Zanzibar/Pemba to work the plantations had reached 30,000 per annum.) Slavery was not abolished until the British made Zanzibar a protectorate in 1890.
The sultan repeatedly promised to end slavery and the slave trade, but never kept his promise. He also used slave labor to transport ivory. He buttressed his position by getting rid of his only rivals, the Mazrui family of Mombassa, Kenya, in 1837. Moreover, he signed huge commercial treaties with America, Britain, and France.
He maintained his position by playing America, Britain, and France against each other. He enforced his authority through wholesale purchases of European and American arms, a navy of 15 ships, and a force of 6,500 soldiers.
Sultan Seyyid Said moved his headquarters from Muscat, Oman, to Zanzibar between 1832 and 1841. In the latter year Zanzibar became the capital of the Omani empire both in Africa and Arabia. The profits from investments in cloves made the sultan and his entourage very rich.
Cloves had become so dominant that many other crops in Zanzibar were cleared away to grow them. The sultan decreed in the 1840s that three clove trees should be planted for every coconut palm. Any landowner failing to do so would have his property confiscated.
By 1841 the sultan appointed his elder son to rule in Oman while he concentrated on Zanzibar. By 1850 Zanzibar/Pemba accounted for 80 percent of world’s clove production. In 1856 the sultan died of dysentery. On his death, his younger son was proclaimed sultan as the new ruler of Zanzibar and the East African coast while the older brother ruled Oman.
The Omani empire had ended, but the Omani dynasty continued until 1890, when Britain took over Zanzibar as a protectorate. The heritage of the Omani empire of East Africa in the first half of the 19th century was a depopulated East and East-Central Africa. The advent of independence in 1964 saw the overthrow of the oligarchy that had grown rich during the heyday of the clove trade.
