On January 1, 1914, the British formally united the Southern Nigeria Protectorate and the Northern Nigeria Protectorate into the Colony and Protectorate of Nigeria. Administratively, Nigeria remained divided into the Northern and Southern Protectorates and Lagos Colony. Inhabitants of the southern region sustained more interaction, economic and cultural, with the British and other Europeans owing to the coastal economy. Following World War II, in response to the growth of Nigerian nationalism and demands for independence, successive constitutions legislated by the British government moved Nigeria toward self-government on a representative and increasingly federal basis. By the middle of the 20th century, a great wave for independence was sweeping across Africa.