The Library of Congress has just published online Sudan: A Country Study, which offers a solid study of Sudan before the separation of South Sudan. Go list of countries and select Sudan.
The book is edited by LaVerle Berry and contains the following chapters:
1. Historical Setting by Tom Ofcansky
2. The Society and Its Environment by Peter Bechtold
3. The Economy by Virginia Delancey
4. Government and Politics by David Shinn
5. National Security by Tom Ofcansky