The north of Sudan is predominantly Muslim, and Arabic-speaking, whereas the south is largely Christian (and animist), with native languages and English being the predominant languages. This demographic faultline has actually been the major source of Sudan's ongoing internal conflict.
A Brief History of the Conflict
Under British colonial rule, Sudan was actually part of Egypt. At the time of British decolonization of the region, the territory was considered being split up into three parts (Egypt, north and south Sudan), as the Muslim/Christian differences were by that time pronounced. Nonetheless, when Egypt was finally granted its independce the territory was left as one. The first prime minister of Sudan, Ismail al-Azhari, was appointed by Egypt and began the northern dominance of the south, which has continued to this day. Al-Azhari began by initiating efforts to make the south Arabic-speaking, and when southern army units retaliated the resistance was immediately squashed. These mutineers moved to the south, further from northern rule, where low-level guerrilla warfare became the norm.
In December 1955, Sudan declared independence from Egypt, but from the beginning suffered economic problems. In 1958, the military decided to take control, having the weapons and organization to do so. Meanwhile Ibrahim Aboud had become the prime minister and followed in al-Alzhari's footsteps in attempting to "islamicize" the south (both in terms of language and culture). Missionaries and Christian schools were shut down, much to the dislike of the people. In 1963, rebellion against Aboud's rule begins to spread, even by some in the north who were in favor of a secular government. As Aboud lost support, he was replaced by Jafar al-Numeiri in a military coup in 1969. By this time, the Southern Sudan Liberation Movement had formed, and provided substantial opposition to northern forces. Finally, after four years of attempted (and failed) suppression by the north, the north agrees to meet with the SSLM. From this meeting came the Addis-Adaba Agreement, which granted autonomy (but not indepence) to the south. At this point, the fighting (mostly) comes to a halt, although the country's economic problems continue without change. The atmosphere in the north becomes more and more extreme, and soon there is significant movement towards adopting sharia (Islamic law) and making Islam a more political force.
In 1983, sharia is adopted by Numeiri for all of Sudan, essentially throwing out the terms of the Addis-Adaba Agreement. Once again, the south retaliates, this time led by John Garang, the leader of the Sudan People's Liberation Army (the military branch of the SSLM). From the start Garang began planning a separate government for the south. This conflict is made worse throughout the 1980's by man-made famine, which forced hundreds of thousands of Sudanese to become refugees.
In 1985, Numeiri is overthrown by a military coup, and after four years of inconstant government, Umar Hassan Muhammad al-Bashir takes control. Al-Bashir believed in a unifed Arabic/Muslim Sudan and intensified Islamic law in the north and the ongoing campaign in the south. While he succeeded in taking many of the larger towns of the south, the countryside was still left largely out of northern control. During this same time period, oil was discovered in the south, further fueling the conflict. During this conflict the Dinka and Nuer become the strongest protesters to northern attempts at dominance.
SPLA & Government
After a history dominated by civil war, in which millions of lives were lost to bombs, bullets, famine and disease, an agreement has recently been reached by the northern government and the SPLA, not only calling for a cessation of hostilities, but also the sharing of the south's oil resources. Leading up to this agreement was substantial international pressure, especially from the United States, whose interest in the Christian south (and its oil reserves), led to its offer to lift sanctions on the country if the war comes to an end. Despite these steps towards peace, there is still ongoing guerilla warfare, and some intensifying confict in the western part of the country. However, this is only a rudimentary outline of where Sudan stands now -- for a more detailed look at the current situation, please explore the links below.
This is a basic, informative CIA website describing the Sudan's general aspects. It is also where the more detailed map is from.
The Washington Post has printed several excellent articles on the effect of oil discoveries and exploitation on exacerbating the civil war, population displacement,and disease.
This website hosts a series of very moving photographs from the famine in southern Sudan in 1998.
A good chronology of key events. The BBC website is worth exploring further as it has a number of excellent updates on current events.