BEFORE INDEPENDENCE:

William Y. Adams - Nubia: Corridor to Africa (1977)

Winston S. Churchill - The River War: An Account of the Reconquest of the Soudan, 3rd ed. (1933, reissued 1973).

Robert O. Collins - King Leopold, England, and the Upper Nile, 1899-1909 (1968); The Waters of the Nile, The Southern Sudan, 1883-1898 (1962), Land Beyond the Rivers: The Southern Sudan, 1898-1918 (1971), and Shadows in the Grass: Britain in the Southern Sudan, 1918-1956 (1983)

O.G.S. Crawford - The Fung Kingdom of Sennar (1951, reprinted 1978)

M.W. Daly - Empire on the Nile: The Anglo-Egyptian Sudan, 1898-1934 (1986), and Imperial Sudan: The Anglo-Egyptian Condominium, 1934-1956 (1991)

Richard Gray - A History of the Southern Sudan, 1839-1889 (1961, reprinted 1978)

Yusuf Fadl Hassan - The Arabs and the Sudan: From the Seventh to the Early Sixteenth Century (1967)

P.M. Holt and M.W. Daly - A History of the Sudan, from the Coming of Islam to the Present Day, 4th ed. (1988).

P.M. Holt - The Mahdist State in the Sudan, 1881-1898: A Study of Its Origins, Development, and Overthrow, 2nd ed. (1970)

Kenneth Henderson - Sudan Republic

Richard Hill -  Egypt in the Sudan, 1820-1881 (1959, reprinted 1986)

Lidwien Kapteijns - Mahdist Faith and Sudanic Tradition: The History of the Masalit Sultanate, 1870-1930 (1985)

Mekki Shibeika (Makki Shibikah) - British Policy in the Sudan, 1882-1902 (1952)

Ahmad Alawad Sikainga - The Western Bahr al-Ghazal Under British Rule, 1898-1956 (1991)

G.N. Sanderson - England, Europe & the Upper Nile, 1882-1899: A Study in the Partition of Africa (1965)

Jay Spaulding - The Heroic Age of Sinnar (1985)

Peter Woodward -  Sudan, 1898-1989

AFTER INDEPENDENCE:
 

Abel Alier - Southern Sudan; Too Many Agreements Dishonoured

Mohamed Omer Beshir - The Southern Sudan: Background to Conflict (1968);
The Southern Sudan: From Conflict to Peace (); Revolution and Nationalism in the Sudan, 2nd ed. (1977)

K.D.D. Henderson - Sudan Republic (1966)

Mansour Khalid - Nimeiri and the Revolution of Dis-May (1985), and The Government They Deserve: The Role of the Elite in Sudan's Political Evolution (1990).

Joseph Oduho and William Deng - The Problem of the Southern Sudan (1963)

Dunstan M. Wai - The African-Arab Conflict in the Sudan (1981)

Gabriel Warburg -  Islam, Nationalism and Communism in a Traditional Society.

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Copies of the journal Sudan Notes and Records always deserve investigation.  The meticulous observations of everyday life by its contributors in the Condominium and early post-independence period can be read on many levels.
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There is no adequate history of the civil war.
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Harold D. Nelson (ed.), Sudan, a Country Study, 3rd ed. (1983), provides basic information on the land, people, economy, and history.