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  , country located in northeastern Africa. The name Sudan derives from the Arabic expression bilād al-sūdān (“land of the blacks”), by which medieval Arab geographers referred to the settled African countries that began at the southern edge of the Sahara. For more than a century, Sudan—first as a colonial holding, then as an independent country—included its neighbour South Sudan, home to many sub-Saharan African ethnic groups. Prior to the secession of the south in 2011, Sudan was the largest African country, with an area that represented more than 8 percent of the African continent and almost 2 percent of the world’s total land area.
  Since ancient times the Sudan region has been an arena for interaction between the cultural traditions of Africa and those of the Mediterranean world. Islam and the Arabic language achieved ascendancy in many northern parts of the region, while older African languages and cultures predominated in the south.
  The country became independent in 1956 and has had numerous changes in government since then. Successive regimes found it difficult to win general acceptance from the diverse political constituencies. An early conflict arose between those northern leaders who hoped to impose unity upon the nation through the vigorous extension of Islamic law and culture to all parts of the country and those who opposed this policy; the latter included the majority of southerners and those northerners who favoured a secular government.
  From 1955 until 1972 there prevailed a costly and divisive civil war, fought largely in the south but punctuated by violent incidents in the north. The Addis Ababa Agreement of 1972 ended the conflict only temporarily, and in 1983 the civil war resumed. By this time the comparative lack of economic development in the south had become a new source of regional grievance, and northern leaders’ continuing attempts to Islamize the Sudanese legal system proved an even more potent source of discord. Attempts to end the civil war included numerous discussions, cease-fires, and agreements but yielded very little success until 2005, when the Comprehensive Peace Agreement ended the warfare. It also granted southern Sudan semiautonomous status and stipulated that a referendum on independence for the south would be held in six years. The results of the vote, held in January 2011, were overwhelmingly in favour of independence, and South Sudan was declared an independent country on July 9, 2011.
  Sudan’s capital, Khartoum, is located roughly in the centre of the country, at the junction of the Blue Nile and White Nile rivers. It is part of the largest urban area in Sudan and is a centre of commerce as well as of government.
  Sudan is bounded on the north by Egypt, on the east by the Red Sea, Eritrea, and Ethiopia, on the south by South Sudan, on the west by the Central African Republic and Chad, and on the northwest by Libya.
  vast plains and plateaus that are drained by the Nile River and its tributaries. This river system runs from south to north across the entire length of the east-central part of the country. The immense plain of which Sudan is composed is bounded on the west by the Darfur and on the east by the Ethiopian Plateau and the Red Sea Hills (ʿAtbāy). This plain can be divided into a northern area of rock desert that is part of the Sahara; the western
  Most of northern Sudan is a sand- or gravel-covered desert, diversified by flat-topped mesas of Nubian sandstone and islandlike steep-sided granite hills. In south-central Sudan the clay plain is marked by inselbergs (isolated hills rising abruptly from the plains), the largest group of which forms the plateau region with flat-topped mesas and buttes. The volcanic highlands of the Marrah Mountains rise out of the sea level. These mountains form the Nile-Congo watershed and the western boundary of the clay plain.
  In northeastern Sudan the Red Sea Hills region is an uplifted escarpment. The scarp slope facing the Red Sea forms rugged hills that are deeply incised by streams. The escarpment overlooks a narrow coastal plain that is 10 to 25 miles (16 to 40 km) wide and festooned with dunes and coral reefs. Farther south the eastern uplands constitute the foothills of the Ethiopian highland massif.
  Drainage and soils
  The Nile River system is the dominant physical feature, and all streams and rivers of Sudan drain either into or toward the Nile. It enters the country as the White Nile (Baḥr Al-Abyaḍ) in the southeast, about 60 miles (100 km) south of Kūstī, and maintains an extremely low gradient until it is joined by the Blue Nile (Baḥr Al-Azraq) at Khartoum. The Blue Nile, which rises in the Ethiopian Plateau, contributes much of the floodwaters of the White Nile. After the confluence of the White and Blue Niles at Khartoum, the river flows in a great northward-curving course and is known simply as the Nile (Nahr Al-Nīl). Throughout much of the country, however, drainage does not reach the Nile; the rivers of the southwest infrequently reach the Baḥr Al-Ghazāl system, and to the north most hill groups initiate seasonal watercourses that are lost in the surrounding plains.
  The surface of the deserts in the north and northeast are either bare rock, a mantle of bare waste, or sandy expanses of mobile dunes known as ergs. In the semiarid zone of north-central Sudan, the layer of rock waste is slightly modified to form immature soils; in the Qawz region, soils are brownish red and of low fertility. Alluvial soils occur at the desert deltas of Al-Qāsh (the Gash) and Barakah rivers, along the White and Blue Niles, and in the alluvial plains of the many small rivers radiating from the Marrah Mountains. The alkaline soils of the south-central plain are heavy cracking clays. The soil of the Gezira (Al-Jazīrah) plain south of Khartoum is deep-cracking uniform clay that has been deposited during the annual inundations of the Blue Nile.
  In northernmost Sudan, northerly winds prevail for most of the year, and rainfall is rare. To the south of this the seasons are characterized by the north-south oscillation of the boundary between moist southerly air and dry northerly air. In winter the north winds of the tropical air mass blow across Sudan. These winds are relatively cool and dry and usually bring no rain. Sometime around May, the moist southerly air of the southern maritime air mass moves northward across the country. Because of this, central and southern Sudan have rainy seasons, the total lengths of which vary according to their latitude.
  Sudan is a hot country. The central and eastern areas have the highest mean annual temperatures, typically ranging from the mid-90s to mid-100s F (mid-30s to low 40s C). In the west and northwest of the country, the highest mean temperatures generally range from the mid-80s to mid-90s F (low to mid-30s C). The highest temperatures normally occur just before the rainy season. The mean minimum temperatures in most of the country range from the high 60s to high 70s F (low to mid-20s C); in the west and northwest, mean minimum temperatures are a little lower, ranging from the high 50s to high 60s F (mid-10s to low 20s C).
  Precipitation varies from almost nothing in the north and centre to 20–30 inches (500–750 mm) annually in the south. Along the Red Sea the climate is alleviated by sea breezes, and most of the rain falls during winter. In southern Sudan, precipitation usually occurs during the summer months. Dust storms are common in the north and centre, often occurring before rainstorms in the late spring and early summer.