The Second Sudanese Civil War started in 1983, although it was a continuation of the First Sudanese Civil War (1955 to 1972). The war took place mostly in southern Sudan and was the longest and deadliest war of the later 20th century. Roughly 1.9 million civilians were killed in southern Sudan, and more than 4 million have been forced to flee their homes at one time or another since the war began.
The war is usually characterized as a fight between the southern and the northern government. Religion is the crucial cause in the conflict. The North, with roughly two-thirds of Sudan land and population, is Muslim and Arabic-speaking; the Northern identity is inseparable integration of Islam and the Arabic language. The South is more native African in race, culture, and religion. Its identity is native African, with Christian influences and Western orientation. 
Another factor in the Second War was the natural resources of Sudan, especially in the South, where there are large oil fields. Oil revenues make up about 70% of Sudan’s export earnings. The South also has major access to the Nile River, and is much more fertile. The North of the country is on the edge of the Sahara desert. The northern inclination to control these resources, as well as southern, contributed to the war.