Sudan, the largest and one of the most geographically diverse states in Africa, split into two countries in July 2011 after the people of the south voted for independence.
The government of Sudan gave its blessing for an independent South Sudan, where people have for decades been struggling against rule by the north.
Sudan has been beset by conflict. Two rounds of north-south civil war cost the lives of 1.5 million people, and a continuing conflict in the western region of Darfur has driven two million people from their homes and killed more than 200,000.
Sudan's centuries of association with Egypt formally ended in 1956, when joint British-Egyptian rule over the country ended.
Independence was rapidly overshadowed by unresolved constitutional tensions with the south, which flared up into full-scale civil war that the coup-prone central government was ill-equipped to suppress.
The military-led government of President Jaafar Numeiri agreed to autonomy for the south in 1972, but fighting broke out again in 1983.
After two years of bargaining, the rebels signed a comprehensive peace deal with the government to end the civil war in January 2005.
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At a glance
Humanitarian crisis: Civil war in Darfur region is seen as “one of the worst nightmares in recent history”; tribal clashes in south have been escalating
Politics: South Sudan seceded in July 2011 after opting for independence in a referendum
International: President Omar Bashir faces war crimes charges over Darfur
Economy: Oil production and revenues have been rising
The accord provided for a high degree of autonomy for the south, and an option for it to secede.
In Darfur, in western Sudan, the United Nations has accused pro-government Arab militias of a campaign of ethnic cleansing against non-Arab locals.
The conflict has strained relations between Sudan and Chad, to the west. Both countries have accused each other of cross-border incursions. There have been fears that the Darfur conflict could lead to a regional war.
Decades of fighting have left South Sudan's infrastructure in tatters. With the return of millions of displaced southerners, there is a pressing need for reconstruction.
The economic dividends of peace could be great. Sudan has large areas of cultivatable land, as well as gold and cotton. Its oil reserves are ripe for further exploitation.
Arabic is the official language and Islam is the state religion, but the large non-Arab, non-Muslim minority has rejected attempts by the government in Khartoum to impose Islamic Sharia law on the country as a whole.
President Omar Bashir has been locked in a power struggle with Hassan al-Turabi, his former mentor and the main ideologue of Sudan's Islamist government. Since 2001 Mr Turabi has spent periods in detention and has been accused, but not tried, over an alleged coup plot.