SUDAN (Arabic Bilad-es-Sudan, country of the blacks), that region of Africa which stretches, south of the Sahara and Egypt, from Cape Verde on the Atlantic to Massawa on the Red sea. It is bounded south (I) by the maritime countries of the west coast of Africa, (2) by the basin of the Congo, and (3) by the equatorial lakes, and east by the Abyssinian and Galla highlands. The name is often used in Great Britain, in a restricted sense, to designate only the eastern part of this vast territory, but it is properly applied to the whole area indicated, which corresponds, roughly, to that portion of negro Africa north of the Equator under Mohammedan influence. The Sudan has an ethnological rather than a physical unity, and, politically, it is divided into a large number of States, all now under the control of European Powers.
Within the limits assigned it has a length of about 4,000 m., ex tending southwards at some points i,000 m., with a total area of over two million square miles, and a population, approximately, of 4o millions. Between the arid and sandy northern wastes and the well-watered and arable Sudanese lands there is a narrow transitional zone of level grassy steppes, partly covered with mimosas and acacias. Otherwise, the Sudan may be described as a moderately elevated region, with extensive open or rolling plains, level plateaux, and abutting, at its eastern and western ends, on mountainous country. Crystalline rocks, granites, gneisses and schists, of the Central African type, occupy the greater part of the country. Toward the south-east, slates, quartz ites and iron-bearing schists occur, but their age is not known.
The Sudan contains the basin of the Senegal and parts of three other hydrographic systems, viz., the Niger, draining southwards to the Atlantic; the central depression of Lake Chad; and the Nile, flowing northwards to the Mediterranean. Lying within
the Tropics, and with an average elevation of not more than 1,500 to 2,000 ft. above the sea, the climate of the Sudan is hot, and, in the river valleys, very unhealthy. Cut off from North Africa by the Saharan desert, the inhabitants, who belong, in the main, to the negro family proper, are thought to have re ceived their earliest civilization from the East. Arab influence and the Muslim religion began to be felt in the western Sudan as early as the 9th century, and had taken deep root by the end of the 11th. The existence of native Christian States in Nubia hindered for some centuries the spread of Islam in the eastern Sudan, and throughout the country some tribes have remained pagan. It was not until the last quarter of the 19th century that the European nations became the ruling force.
The terms western, central and eastern Sudan are indicative of geographical position merely. The various States are politically divisible into four groups : (I) Those west of the Niger; (2) those between the Niger and Lake Chad; (3) those between Lake Chad and the basin of the Nile; (4) those in the upper Nile valley.
The first group fell under the control of France at the end of last century, and are now included in Senegal and French Sudan. (See SENEGAL; SUDAN, FRENCH; also FRENCH WEST AFRICA.) The second group of Sudanese States is almost entirely within the British protectorate of Northern Nigeria. The third, or central group of Sudanese States, is included in French Equatorial Africa (q.v.). The fourth group consists of the States conquered during the 19th century by the Egyptians, and now under the joint con trol of Great Britain and Egypt. These countries are known col lectively as the Anglo-Egyptian Sudan (see below).