The separation movement between north and south Sudan started more than five decades ago.
The population of North Sudan are mostly Muslim and speak Arabic, whereas the south is mainly Christian and animist, and still abides by tribal allegiances.
Northern Sudan reaped the benefits of Egyptian colonisation in the 19th Century, and as a result is more populated, urbanised and has greater infrastructure than the south.
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However, the south is resource-rich, and has a number of oil reserves.
These difference meant that the south has engaged in a seccession movement from 1955, when Sudanese defence personnel in the southern regions of the country mutinied.
Since then there have been two separate conflicts: the first and second Sudanese civil wars. The first lasted from 1955 to 1972, and the second from 1983 to 2005.
At least two million people were killed in the war and resulting famine, and a further four million southern Sudanese were displaced by the conflict.
The conflicts between the north and south official ended in 2005, when a treaty was signed between the Sudan People's Liberation Movement (SPLM) and the government of Sudan.
Part of the treaty was an agreement between the two parties to share oil revenue and set a timetable for a referendum on South Sudan's independence.
