The period's "closed door" ordinances, which barred northern Sudanese from entering or working in the south, reinforced this separate development policy. Moreover, the British gradually replaced Arab administrators and expelled Arab merchants, thereby severing the south's last economic contacts with the north. The colonial administration also discouraged the spread of Islam, the practice of Arab customs, and the wearing of Arab dress. At the same time, the British made efforts to revitalize African customs and tribal life that the slave trade had disrupted. Finally, a 1930 directive stated that blacks in the southern provinces were to be considered a people distinct from northern Muslims and that the region should be prepared for eventual integration with British East Africa.