Darfur is a desperately poor region in a poor country, with some of the highest infant mortality rates and lowest education levels in Sudan.
Tensions boiled over in 2003, just as the north-south conflict was starting to wane, and local Darfuris took up arms to force Khartoum to deliver greater autonomy and better governance.
Among the greatest sources of tension is access to water, and it is no accident that the dividing line between combatants was drawn between disaffected farmers on one side and nomadic herders on the other.
Both had long coexisted, with farmers allowing herdsmen to graze their flocks on the stubble after harvest time. But as those agreements gradually fell apart, and when farmers took up arms against the state, the state armed the nomads into marauding militias called janjaweed.
Loyalty among these groups has shifted over time, of course, and some Arabic-speaking nomads have shifted their support to rebel groups, while some rebel groups have fought among themselves.
The conflict in Darfur, in which all combatants – Arab and non-Arab – are Muslims is not to be confused with the 20-year civil war in South Sudan, where the Muslim-dominated government in Khartoum fought against a Christian-dominated South. An estimated 1.5 million people died in that conflict between 1983 and 2005, more than four times as many as those killed in Darfur.
Human rights activists, the US administration of George W. Bush, and the International Criminal Court chief prosecutor Luis Moreno-Ocampo have all called Darfur a "genocide"; but despite the higher death toll in South Sudan, that conflict is seen as a mere civil war.