Zanzibar came under Omani authority, with the Portuguese expelled and Omani influence consolidating across key ports and islands. Under this expanding Omani maritime sphere, slave and ivory commerce intensified, laying foundations for Zanzibar’s later plantation-and-slave-trading economy.
After a siege lasting nearly three years, Omani forces captured Fort Jesus at Mombasa, a major Portuguese stronghold on the Swahili Coast. This victory accelerated the decline of Portuguese influence and strengthened Omani power over coastal trade networks that fed into Zanzibar’s later role as a major entrepôt for enslaved people and commodities.
Omani authorities constructed the Old Fort (Ngome Kongwe) in Stone Town on the site of a former Portuguese chapel, symbolizing the durable shift in power and providing an enduring military-administrative footprint for Omani rule on Zanzibar.
Ahmad bin Said established the Al Bu Said dynasty in Oman, the ruling house that would later anchor Oman’s Indian Ocean empire and its governance in Zanzibar. The dynasty’s consolidation enabled more sustained political and commercial engagement with the Swahili Coast.
Cloves were introduced to Zanzibar in the early 19th century and soon became central to plantation expansion. The resulting demand for labor helped intensify the importation and exploitation of enslaved Africans in the Omani-Zanzibari economy.
Britain and Sayyid Said concluded the Moresby Treaty, aiming to curb the Indian Ocean slave trade by limiting slave exports from Omani East African dominions to British-controlled areas and restricting sales to Christians. It marked an early diplomatic constraint on Zanzibar-linked slave trafficking, though enforcement remained difficult.
Said bin Sultan moved his capital/court from Muscat to Stone Town, making Zanzibar the political and commercial hub of his western Indian Ocean dominions. This shift supercharged plantation agriculture (especially cloves) and tied Zanzibar even more tightly to mainland slave-raiding and caravan networks supplying coerced labor.
Britain and the Omani state signed the Hamerton Treaty, restricting the export of enslaved people from Zanzibar toward the Persian Gulf region. The agreement reflected growing British abolitionist pressure, while also exposing persistent enforcement gaps and continued trafficking through legal and illegal channels.
Said bin Sultan died, precipitating a succession struggle that led to the separation of his realms: Zanzibar under Majid bin Said and Oman under Thuwaini bin Said. The split institutionalized Zanzibar’s distinct sultanate, whose wealth remained deeply tied to plantation production and enslaved labor.
Majid bin Said became the first Sultan of Zanzibar, formalizing the political separation from Oman. Under his rule, Zanzibar continued to function as a key node in the regional economy—linking clove plantations, ivory commerce, and coerced labor drawn from the East African mainland.
Under British pressure, Zanzibar accepted additional restrictions that confined legally permitted slave movements to specified portions of the coast and reduced the outward flow toward Arabia. The continuing existence of a legal internal trade (and widespread evasion) nonetheless sustained Zanzibar’s coerced-labor plantation system.
Sultan Barghash signed the Frere Treaty, which prohibited the import of enslaved people into Zanzibar and compelled the closure of Stone Town’s open slave market. The treaty empowered more aggressive naval interdiction, significantly damaging (though not immediately ending) the Indian Ocean slave trade routes connected to Zanzibar.
Britain and Germany signed the Heligoland–Zanzibar Treaty, clarifying spheres of influence in East Africa. Germany recognized British authority in Zanzibar, reinforcing the protectorate-era political conditions under which Britain pressed anti-slavery measures and reshaped Zanzibari sovereignty.
An anti-slavery decree (issued under Sultan Ali bin Said) confirmed prior measures against the slave trade and placed new legal framing around slavery and emancipation. It reflected the growing entanglement of abolition with protectorate governance, while leaving many enslaved people in coerced dependency.
A brief British bombardment ended a succession crisis and installed a ruler aligned with British policy. The episode dramatically demonstrated the limits of Zanzibari autonomy under the protectorate system—conditions that soon facilitated deeper intervention in slavery’s legal status.
British authorities forced the Sultan to end slavery’s legal standing in Zanzibar, initiating a prolonged, bureaucratic emancipation process (including manumission applications) that unfolded unevenly across Unguja and Pemba. Coercion and dependency persisted in practice, but the decree marked a decisive legal turning point.
By 1909, abolition enforcement was extended to include enslaved concubines, closing a major loophole in earlier emancipation policy. This is often treated as the completion of Zanzibar’s long transition from a slave society to post-slavery labor arrangements under colonial oversight.
Omani Zanzibar: East African Enslavement and the Indian Ocean Trade (18th–19th centuries)
