 The Anti-Slavery Society estimated that there were 2,000,000 slaves in the early 1930s, out of an estimated population of between 8 and 16 million.It was finally abolished by order of emperor Haile Selassie on 26 August 1942.When British rule was first imposed on the Sokoto Caliphate and the surrounding areas in northern Nigeria at the turn of the 20th century, approximately 2 million to 2.5 million people there were slaves.