The Egyptians conquered Sudan in 1874 and established the province of Equatoria. Islamic Mahdist revolutionaries entered the territory in 1885, but British troops defeated the invaders and took over Sudan in 1898. (Britain had occupied Egypt since 1882.) Britain and Egypt ruled the country in conjunction as Anglo-Egyptian Sudan. In the early 20th century, Christian missionaries converted a large segment of the population and introduced English to the region. The result was a clearly defined line between the Arab north and the black African animists and Christians in the south.

Egypt and Britain ruled Sudan until 1953, when Anglo-Egyptian Sudan was granted Sudan self-government. In 1955, army officers in the south mutinied, sparking a civil war between the north and south. Southerners accused the government, based in the north, of trying to force Islamic and Arab culture on the south. In addition, the south said the government reneged on promises to grant the south more autonomy through a federal system of government. Independence was proclaimed on Jan. 1, 1956, and the civil war dragged on until the 1972 signing of the Addis Ababa Agreement. About 500,000 people died in the war. Under the accord, the Southern Sudan Autonomous Region was formed.

War broke out again in 1983 when President Gaafar Mohamed Nimeiri abrogated the treaty and declared all of Sudan a Muslim state, ruled by shariah, or Islamic law. In response, southern rebels formed the Sudan People's Liberation Army (SPLA) and fought the government for more than two decades. Government troops unleashed vicious massacres against civilians and entire villages. The government also provoked internecine violence between tribes and ethnic groups. A cease-fire was declared between the Sudanese government and the SPLA in July 2002. During peace talks, the government agreed to a power-sharing government for six years, to be followed by a referendum on self-determination for the south. Fighting on both sides continued throughout the peace negotiations

On Jan. 9, 2005, after three years of negotiations, a peace deal was reached between the southern rebels, led by John Garang of the SPLA, and the Khartoum government, ending Africa's longest-running civil war. Under the deal, roughly half of Sudan's oil wealth was given to the south, as well as nearly complete autonomy and the right to secede after six years. But just two weeks after Garang was sworn in as first vice president as part of the power-sharing agreement, he was killed in a helicopter crash during bad weather. Rioting erupted in Khartoum, killing nearly 100. Garang's deputy, Salva Kiir, was quickly sworn in as the new vice president, and both north and south vowed that the peace agreement would hold.

In July 2009, an international tribunal at The Hague redefined the border of Sudan's oil-rich Abyei region, giving the North rights to the lucrative Heglig oil field, and the South retained rights to other large oil fields in Abyei.

In April 2010 elections, Salva Kiir, head of the Sudan People's Liberation Movement, was reelected president of the semi-autonomous South, taking 93% of the vote. He opted not to run for national president, choosing instead to remain the leader of southern Sudan — leaving no doubt that he supported independence.
 

Historic Vote for Independence

In a historic seven-day secessionist referendum that began in southern Sudan on January 9, 2011, 98.8% of voters chose independence from the north. Sudan's president Omar al-Bashir accepted the results and said he would not seek reelection when his term expires in 2015.

The Bush administration negotiated the 2005 Comprehensive Peace Agreement, which in addition to setting the date of the referendum also called for people in the contested region of Abyei to participate in the vote. That vote, however, has been delayed because a decision on what constitutes a resident of Abyei has not been reached. Tribal leaders in the region have made it clear that their loyalty lies with the south, but there has not been a date set for a vote in Abyei. Any declaration of affiliation with the south by Abyei could trigger an attack from the north. Abyei sits between northern and southern Sudan and has historically served as a bridge between the two. When voting began in southern Sudan, at least 23 people died in Abyei, confirming speculation that the region continues to be a matter of contention. In May 2011, armed forces from Sudan seized control of Abyei, which the south Sudanese government called an act of war. More than 20,000 people fled and the United Nations sent an envoy to intervene.

In July 2011, after years of fighting, the Republic of South Sudan declared its independence and became Africa's 54th state. Thousands celebrated in the streets of South Sudan's capital, Juba. Kiir, South Sudan's president, signed the interim Constitution. However, even as South Sudan celebrated its independence, Abyei's uncertainty was only one obstacle that awaits the fledgling state. South Sudan becomes one of the poorest countries in the world with half of the population living on less than $1 per day and an adult literacy rate of less than 25%. South Sudan also needs to establish a new government and constitution.

Instability and conflict with Sudan over oil plagued South Sudan since independence. Sudan launched air attacks into South Sudan, the north accused the south of arming militants in the north, and both accused each other of inciting a border war. Tension between the two nations peaked in early 2012 as the economies in both countries continued to shrink and a food crisis intensified in the south, emphasizing the need for oil revenues. As a full-scale war loomed, the two sides negotiated a non-aggression agreement under pressure from the African Union, the U.S., and China. Within days, however, South Sudan accused the north of violating the agreement.

The countries teetered on the brink of border war in April 2012. South Sudan took over disputed oil fields in Heglig, a move the African Union and the UN called illegal. Both sides traded ground and aerial attacks, and Sudan's president Omar al-Bashir said South Sudan he would not negotiate with South Sudan because it only responds to "the gun and bullets." The South withdrew from the contested region, but the aggression continued, prompting the African Union to give the two sides three months to resolve the issues over oil and the disputed border.

July 9, 2012 marked the one-year anniversary of South Sudan's independence. There was little to celebrate as tensions persist and the biggest issues—the border and oil—remain not only unresolved, but a source of violent outbreaks. African Union-sponsored talks have taken place, but both countries face sanctions from the U.N. Security Council if compromise is not achieved by Aug. 2.