... and British involvement

In Oman a new sultan, Sultan bin Ahmed, came to power in 1792. He needed a strong ally to help him combat the Mazrui of Mombasa and also to keep the Persians out of Oman. He found this ally in Britain, by this time a powerful maritime nation with an empire expanding all over the world. In the late 18th century, Britain was at war with France and knew that the French emperor, Napoleon Bonaparte, was planning to march through Persia and capture Muscat, on his way to invade India. In 1798 Britain and Oman agreed a Treaty of Commerce and Navigation. Sultan bin Ahmed pledged himself to British interests in India, and his territories became out of bounds to the French. He allowed the British East India Company to establish a trading station in the Persian Gulf, and a British consul was posted to Muscat.

As well as defeating Bonaparte, the British had another motive for the treaty with Oman: they wanted to put pressure on the sultan to end slavery, which had been declared illegal in England in 1772. At this time, the trade from Africa to Oman was still buoyant.
At the same time, Zanzibar's position as an important trade centre was bolstered further when the supply of ivory from Mozambique to India collapsed because of excessive Portuguese export duties. The traders simply shipped their ivory through Zanzibar instead.