Prior to autonomy and eventual independence, Southern Sudan was a region of the Republic of Sudan, which had achieved independence from the co-rule of Great Britain and Egypt in 1956. Sudan had been divided culturally and ethnically between the majority-Muslim Arab north and the majority-Christian Nilotic south. Southern leaders and members of the Sudan Defense Force cited oppression of the North as reason for growing tensions between the two regions. This led to the formation of the separatist Anyanya rebel army, who sought regional autonomy. The First Sudanese Civil War was a 16 year conflict between the Anyanya and the Sudan People's Armed Forces.