Claiming the coastal strip, Omani Sultan Said bin Sultan moved his capital to Zanzibar City in 1840. During this time, Zanzibar became the centre for the east African slave trade. Between 65 and 90 per cent of the Arab-Swahili population of Zanzibar was enslaved. One of the most infamous slave traders on the East African coast was Tippu Tip, who was the grandson of an enslaved African. The Nyamwezi slave traders operated under the leadership of Msiri and Mirambo. According to Timothy Insoll, "Figures record the exporting of 718,000 slaves from the Swahili coast during the 19th century, and the retention of 769,000 on the coast." In the 1890s, slavery was abolished.