British occupation did not significantly change African society within the protectorate until the First World War, with most people continuing to live under the social and political systems that existed before 1891. No attempt was made to remove or limit the powers of the Yao, Ngoni or Makololo chiefs (who had first entered the area in the 19th century) over the original inhabitants they had displaced, subjugated or assimilated, although the Swahili slave traders had been killed in the warfare of the 1890s or had left. One area in which early efforts to change the system manifestly failed was that of domestic slavery. Although slave-trading had been eliminated, and Johnston issued instructions that domestic slaves were to be emancipated, this particular form of slavery endured, particularly in the Central Region, well into the first quarter of the 20th century