Sudan split in two on 9 July 2011, when South Sudan became an independent country after a referendum in which 98.83 per cent of voters chose separation. The partition removed roughly 640,000 square kilometres from what had been Africa's largest country, cost Khartoum about three-quarters of its oil production, and left a border of some 2,000 kilometres that has still not been fully demarcated.
What Happened on 9 July 2011
At midnight, the Republic of South Sudan came into being with its capital at Juba. It became the 193rd member of the United Nations five days later and joined the African Union shortly after, taking the continent's total to 54 recognised states.
Sudan, under President Omar al-Bashir, formally recognised the new state the day before independence — the first country to do so. The recognition was pragmatic rather than gracious: Khartoum had signed a peace agreement six years earlier that committed it to the referendum, and the outcome had never been in doubt.
The numbers that changed hands were substantial. Sudan went from roughly 2.5 million square kilometres to about 1.86 million, losing its position as Africa's largest country to Algeria. It lost around 8 million people and, critically, the oilfields that had underwritten a decade of growth.
The Colonial Line That Made Two Sudans Out of One
The division of 2011 followed a line drawn a century earlier, and understanding it requires going back to the Anglo-Egyptian Condominium that governed Sudan from 1899 to 1956.
Britain administered the territory as two effectively separate entities. The northern provinces — Arabic-speaking, predominantly Muslim, oriented toward Egypt and the Red Sea — received investment in railways, irrigation and the Gezira cotton scheme. The southern provinces — home to Dinka, Nuer, Shilluk and dozens of other Nilotic peoples, following traditional religions or, increasingly, Christianity brought by missionaries — were governed under a different logic entirely.
The Closed Districts Ordinance and the associated "Southern Policy", formalised in the 1920s and 1930s, restricted movement between north and south, discouraged the spread of Arabic and Islam in the south, and encouraged English and Christian mission education instead. The stated intention was protective. The practical effect was to develop two populations with different languages, religions, legal systems and administrative traditions inside one set of borders — and to leave the south with almost no infrastructure, since investment went overwhelmingly north.
Britain reversed course abruptly. At the 1947 Juba Conference it decided the south would be joined to the north in a single independent state, a decision taken with minimal southern consultation. When independence came on 1 January 1956, the new government in Khartoum was dominated by northern elites, and southern demands for federalism went unmet.
Two Civil Wars and the Comprehensive Peace Agreement
Fighting began before independence was even formal. A mutiny by southern soldiers at Torit in August 1955 opened the First Sudanese Civil War, which ran until 1972 and killed an estimated 500,000 people. It ended with the Addis Ababa Agreement, which granted the south regional autonomy and produced eleven years of relative peace.
That settlement collapsed in 1983. President Jaafar Nimeiry dissolved the southern regional government, redrew boundaries in ways that would have placed newly discovered oilfields under northern administration, and imposed sharia law nationwide. The Second Sudanese Civil War followed, led on the southern side by the Sudan People's Liberation Movement/Army under John Garang. It lasted 22 years, until 2005, and is among the deadliest conflicts since the Second World War: estimates run to roughly two million deaths, most from famine and disease rather than combat, with some four million people displaced.
The Comprehensive Peace Agreement, signed at Naivasha in January 2005, ended it. Its central bargain was a six-year interim period of autonomy under a Government of Southern Sudan, a 50-50 split of oil revenue from southern fields, and — the provision that decided everything — a referendum on independence at the end of the term.
John Garang, who had argued for a reformed united Sudan rather than secession, became first vice-president. He died in a helicopter crash in July 2005, three weeks into the job. His successor Salva Kiir favoured separation, and the death removed the most credible advocate for unity on the southern side.
The Referendum and the 98.83 Per Cent
Voting ran from 9 to 15 January 2011. Turnout was around 97.6 per cent of registered voters, and the result was 98.83 per cent for separation — one of the most lopsided margins in any internationally supervised referendum. International observers, including a Carter Center mission, judged the process credible.
The Comprehensive Peace Agreement had committed both parties to making unity "attractive" during the interim period. Very little was done to that end. Khartoum invested little in the south, the promised oil revenue transfers were disputed throughout, and the accumulated grievance of half a century of war left almost no constituency for staying.
Abyei, Heglig and the Border That Was Never Finished
Independence settled sovereignty but not geography. Several stretches of the roughly 2,000-kilometre border remain undemarcated, and the disputes are concentrated where oil, grazing land and water coincide.
Abyei is the most intractable. This roughly 10,500-square-kilometre area was to hold its own simultaneous referendum on which country to join. That vote never took place, because the two sides could not agree on who was eligible: the Ngok Dinka are settled residents aligned with the south, while the Misseriya are Arab pastoralists who migrate through seasonally with cattle and are aligned with the north. Sudanese forces occupied Abyei in May 2011, weeks before independence, and a UN Interim Security Force has been deployed there since. Its status is still unresolved.
Heglig, an oil-producing area awarded to Sudan by a 2009 Permanent Court of Arbitration ruling, was seized by South Sudanese forces in April 2012, bringing the two countries close to full war before South Sudan withdrew under international pressure. Other contested zones include Kafia Kingi, the Kaka area, and stretches along the White Nile.
The border also cuts across long-established pastoral migration routes. Herders who moved seasonally between wet-season grazing in the north and dry-season pasture in the south now cross an international frontier, and the resulting friction produces recurrent local conflict independent of what governments agree.
Oil: The Resource That Split Unevenly
The economic logic of the partition was brutal and simple. Roughly three-quarters of the former Sudan's oil production lies in South Sudan. Essentially all of the infrastructure needed to sell it — the pipelines, the Khartoum refineries, and the export terminal at Port Sudan on the Red Sea — lies in Sudan.
South Sudan is landlocked and had no alternative route. Its only outlet ran through the territory of the state it had just left. Negotiations over transit fees failed, and in January 2012 South Sudan shut down its entire oil production rather than accept Khartoum's terms — an extraordinary decision for a country deriving the large majority of government revenue from oil. The shutdown lasted over a year, devastating both economies, and was resolved only through African Union mediation.
Neither country recovered well. Sudan lost the revenue base that had funded a decade of growth and entered a prolonged fiscal crisis, contributing to the protests that removed Bashir in 2019. South Sudan descended into its own civil war in December 2013, barely two years after independence, in a conflict between factions aligned with Kiir and former vice-president Riek Machar that killed an estimated 400,000 people. Sudan itself returned to full-scale war in April 2023.
How Sudan's Split Compares With Other Modern Partitions
Secessions that produce widely recognised states are rare. South Sudan and Eritrea, which separated from Ethiopia in 1993, are the only two in post-colonial Africa, and both followed the same template: decades of armed struggle, a negotiated settlement, and a referendum with an overwhelming margin. Eritrea's 1993 vote returned 99.8 per cent for independence — and, like Sudan's, was followed by war between the two states within a few years, in Eritrea's case from 1998 to 2000.
Against Czechoslovakia's 1993 dissolution, the contrast is total. The Velvet Divorce was negotiated between political leaderships, involved no referendum and no violence, and produced two states that both joined the European Union and maintain close relations.
Against India and Pakistan in 1947, the parallels are closer but the timescale differs sharply. Both partitions divided territory along lines shaped by colonial administrative practice and religious demography; both left disputed regions — Kashmir, Abyei — unresolved for decades. But Partition was executed in weeks and displaced perhaps 15 million people almost immediately, where Sudan's took six years of implementation after a formal peace agreement.
The lesson common to all of them is that the referendum is the easy part. Drawing a line on a map settles which flag flies; it does not settle who owns the oil, who may graze cattle where, or how a landlocked state reaches the sea. South Sudan's subsequent trajectory is set out in our South Sudan country guide, and the state it left behind in the Sudan country guide.