History of Sudan
The modern Republic of Sudan was formed in 1956 and inherited its boundaries from Anglo-Egyptian Sudan, established in 1899. For times predating 1899, usage of the term "Sudan" for the territory of the Republic of Sudan was somewhat anachronistic, and may have referred to the more diffuse concept of the Sudan.
Second Sudanese Civil War
Islamic fundamentalists in the north had been discontented with the Addis Ababa Agreement, which gave relative autonomy to the non-Islamic majority Southern Sudan Autonomous Region. The fundamentalists continued to grow in power, and in 1983 President Nimeiry declared all Sudan an Islamic state, terminating the Southern Sudan Autonomous Region.