Like the conflict in Darfur, the conflict between north and south Sudan was based on a failure of the elite in the capital, Khartoum, to share power and to extend the benefits of government to the south.
In 1983, a southern group called the Sudanese People’s Liberation Army, led by John Garang, took up arms to replace the northern Arabic-speaking elite with a more broadly representative and secular government.
The war, which claimed 1.5 million lives and displaced millions more, ended only in 2005 with a Comprehensive Peace Agreement between the Khartoum government and the SPLM in Juba.
The agreement created a five-year-long power-sharing arrangement in which Khartoum and Juba share control of power and also share equally in the oil revenues from oil fields that run beneath the north-south boundary. However, it is widely estimated that 70 percent of all oil reserves and oil production occurs in territory under southern control.
The peace agreement allows the south to secede through a 2011 referendum, and polls suggest that most southerners will vote for secession. This would increase Juba's oil revenues by 20 percent and nearly cut Khartoum's revenues in half.
The one thing that could cause a return to war would be division of oil resources.