In the late 1700s, the Omani (Busaidi) state strengthened its influence over the Swahili Coast’s port cities and trade routes. This set the political framework for a plantation economy in Zanzibar that would rely heavily on enslaved labor. The region’s commerce linked mainland East Africa to Indian Ocean markets for labor and export crops.
Cloves were introduced to Zanzibar in the early 1800s and quickly became a high-value export crop. Because clove trees take years to mature, plantation owners invested early in land clearing and long-term labor control. This helped push Zanzibar toward a plantation model where enslaved workers provided much of the workforce.
In September 1822, the Moresby Treaty between Britain and Sultan Saʿīd aimed to limit slave exports linked to Omani-controlled East Africa. It did not end slavery in Zanzibar, but it changed the legal environment around the external slave trade. Over time, these restrictions interacted with plantation expansion, reshaping how enslaved labor was sourced and used.
Sultan Saʿīd ibn Sulṭān increasingly focused on East African commerce and made repeated visits to Zanzibar, strengthening Omani authority and revenue collection there. These moves helped shift economic power toward the islands and coastal trade. They also laid the groundwork for large-scale agriculture aimed at export markets.
During the 1830s and early 1840s, high global clove prices drove rapid expansion of plantations on Zanzibar and Pemba. Planters cleared land and increased purchases of enslaved laborers to plant, weed, and harvest cloves. This created a tighter link between export agriculture and mainland slave-raiding and trading networks.
In 1840, Sultan Saʿīd moved his capital from Muscat to Zanzibar, reflecting the islands’ growing importance in trade and plantation wealth. The move strengthened Zanzibar’s role as a political center for Omani power in East Africa. It also helped institutionalize systems that supported plantation slavery and long-distance commerce.
In 1845, the Hamerton Treaty restricted the export of enslaved people from Zanzibar to the Persian Gulf. While enforcement was uneven and slavery within Zanzibar continued, the treaty marked stronger external pressure on the trade. Plantation owners still relied on enslaved labor, and restrictions often shifted trade routes rather than ending coercion.
Saʿīd ibn Sulṭān died in 1856, and rivalry among his sons led to a political struggle over control of the empire. This uncertainty mattered economically because Zanzibar’s plantation system and slave-based production depended on stable elite rule. British mediation became more important as local leaders sought international backing.
In 1861, British arbitration (the Canning Award) formally divided the Omani realm into two states: Zanzibar (with its East African possessions) and Muscat and Oman. The split reinforced Zanzibar’s identity as a plantation-and-trade sultanate. It also increased British leverage over Zanzibar’s policies, including anti-slave-trade measures.
In 1873, Sultan Barghash signed the Frere Treaty with Britain, banning the import of enslaved people into Zanzibar and forcing the closure of the open slave market in Stone Town. This was a major turning point in the public-facing slave trade. However, it did not immediately end slavery on plantations, and illegal trafficking continued.
On July 1, 1890, the Helgoland–Zanzibar (Zanzibar) Treaty defined British and German spheres of influence in East Africa. This agreement is commonly linked to Zanzibar becoming a British protectorate, tightening British control over foreign relations and policy direction. The new political reality increased pressure for anti-slavery laws to be written and enforced.
In 1890, Sultan Ali bin Saʿid issued a written decree confirming earlier measures aimed at stopping the slave trade. The decree illustrates how abolition policy became a legal and administrative project, not only a naval one. It also shows that anti-slavery action involved negotiation and conflict among the sultan, local elites, and British officials.
On April 6, 1897, Sultan Hamoud bin Mohammed issued an abolition decree making slavery illegal in Zanzibar under British pressure and oversight. This did not instantly transform plantation labor, but it changed the legal basis of coercion. Former enslaved people could pursue manumission (legal recognition of freedom) through new administrative channels.
After 1897, British-run courts and administrators processed applications for manumission, and many people sought formal freedom between 1897 and 1909. In practice, plantation production often continued through dependency, debt, and social pressure, and some forms of bondage (including concubinage) were treated differently under policy. This period shows how ending slavery involved years of legal work and everyday struggle, not a single clean break.
Swahili Coast and Zanzibari Clove Plantation Slavery (1780–1890)