The Bartle Frere Mission addressed the issue of the Zanzibar slave trade between the Swahili coast in Zanzibar and Oman in the Arabian Peninsula, which was at the time the major part of the ancient Indian Ocean slave trade.
An agreement with the British in 1867 further restricted the slave trade to be legal only from the mainland to the Sultanate of Zanzibar itself.
The Frere Treaty of 1873 banned all further import of slaves from the African mainland to the Zanzibar Archipelago.
The treaty resulted in the closure of the open slave market in the Zanzibar Stone Town.
The treaty was therefore a considerable mile stone in the combat against the Indian Ocean slave trade.