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.
Flag of South Sudan
When Sudan became independent in 1956, the predominantly Christian people living in the south of the country had no regional symbols, while the already dominant Muslim north displayed Islamic symbols on the national flag. Before independence, the British government had arranged for appropriate local symbols for the regions in Sudan, but the new government in independent Sudan had opposed the use of these symbols as being counterproductive to fostering national unity.