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.
Anglo-Egyptian conquest of Sudan
The Anglo-Egyptian conquest of Sudan in 1896–1899 was a reconquest of territory lost by the Khedives of Egypt in 1884 and 1885 during the Mahdist War. The British had failed to organise an orderly withdrawal of Egyptian forces from Sudan, and the defeat at Khartoum left only Suakin and Equatoria under Egyptian control after 1885. The conquest of 1896-99 defeated and destroyed the Mahdist state and re-established Anglo-Egyptian rule, which remained until Sudan became independent in 1956.