"Divided they stand" is a three-part series on Sudan, covering the lead-up to January's referendum vote on the South's independence, the divisions that are already pulling the country in two and the rise of Juba, South Sudan's capital in the making.

JUBA, South Sudan — On a large-scale map the military official pointed to a section of the 1,300-mile border that separates Sudan’s North and South, identifying it as a "hot spot" where fighting might break out. Then he pointed to another, and another.

Already there are reports of additional troops being redeployed to the unclear and un-demarcated border that may soon separate two sovereign nations rather than mark two parts of a single state.

Southern Sudan’s 9 million people are preparing to vote in a referendum in January that will likely result in the splitting of Africa’s biggest country, but with the North reluctant to let the oil-rich South go fears are growing that the vote might reignite one of Africa’s longest-running civil wars.

The omens are not good and the United States is spearheading international efforts to prevent a resumption of the North-South fighting. January’s referendum is the final stage of the internationally brokered Comprehensive Peace Agreement struck in 2005 to end 22 years of civil war that killed 2 million people and forced millions more from their homes.

U.S. Secretary of State Hillary Clinton has described Sudan as “a ticking time bomb” and she has called a vote for separation “inevitable.” In November she told the U.N. Security Council that a peaceful vote was essential.

“The alternative, the unacceptable alternative, is Sudan’s past,” she said, “more than four decades of recurring conflict, 2 million people dead, millions more displaced, simmering tensions that stall development and perpetuate poverty, then erupt again to darken the lives of another generation of Sudanese children.”

Washington has offered to remove Sudan from a list of state sponsors of terror and to restore normal diplomatic ties with Khartoum if it allows the peaceful conduct of the referendum.

Despite a joint statement saying that “war is not an option” issued by defense ministers in Khartoum and Juba on Nov. 11, the two sides have been trading accusations, and occasional gunfire, since.

The day after the communique the northern Sudan Armed Forces (SAF) accidentally dropped a bomb in the South while battling rebels from the western region of Darfur. A senior official in Khartoum’s National Congress Party (NCP) later accused the semi-autonomous government of southern Sudan of backing the rebels. “We think this is a declaration of war against the North,” said Mandour al-Mahdi, the NCP official.

The Sudan Peoples’ Liberation Movement denies supporting the rebels and retorted that a northern helicopter gunship had attacked southern army positions.

The allegations and counter-claims sour already difficult relations between North and South. The two sides have so far failed to agree on key issues including border demarcation and the sharing of revenues from an estimated 6 billion barrels of oil, 80 percent of which is found in the South, as well as citizenship and the status of the disputed oil-producing region of Abyei where a separate vote is supposed to be held on whether it will choose to join the North or South.

Added to the undoubted human catastrophe of any conflict, a return to war in Sudan might cost more than $100 billion, according to a study published in November.

“War is very expensive,” said Matthew Bell, associate director at Frontier Economics, who carried out the research. “Sudan has huge potential but if there is a conflict you set it back a generation at least.”

Bell told GlobalPost that a resumption of war could cost Sudan $50 billion in lost economic growth over 10 years. He said its regional neighbors — Kenya, Ethiopia and Uganda — could lose around $25 billion, the same amount that international humanitarian aid and peacekeeping might cost in the event of conflict.

Activists are urging the international community to work now to avoid paying the price later.

“Failure to act in time to ensure a peaceful referendum in South Sudan risks having devastating consequences for Sudan and for the whole region,” warned Louise Roland-Gosselin, executive director of Waging Peace.

Diplomatic pressure is building. Late in November the Intergovernmental Authority on Development, a six-nation regional grouping made up of Djibouti, Ethiopia Kenya, Somalia, Sudan and Uganda, discussed the coming referendum at a one-day summit in the Ethiopian capital Addis Ababa. The meeting’s host Prime Minister Meles Zenawi said that war was “possible but not inevitable.”

“Like all doomsday scenarios [a return to war] is too ghastly to contemplate,” he said.

Chairing a special meeting on Sudan at the U.N. in November, Britain’s Foreign Minister William Hague said this is “a defining moment” for Sudan. “In the coming months, there will be few greater challenges for the international community, the United Nations and the Security Council than Sudan,” he said.

The U.N. is mulling whether to send an additional 2,000 peacekeepers to join the 10,000 already deployed in the South as part of the U.N. Mission in Sudan. But Secretary-General Ban Ki-Moon warned: “The presence of U.N. troops will not be enough to prevent a return to war should wide-spread hostilities erupt.”

Observers welcome the diplomatic moves but are concerned that time is running out to ensure the peaceful passage not just of the vote on Jan. 9, but its aftermath, expected to include the difficult partition of Africa’s biggest country. “This doesn’t end with independence for the South,” said Kenneth Mpyisi, a director at the Institute for Security Studies in Nairobi.

In a report last month the International Crisis Group warned of conflict if talks over the shape of the future North-South relationship fail to resolve the many sticky outstanding issues.

“There is a lot of focus on the referendum itself, but we need to look beyond that,” said Zach Vertin, a Crisis Group analyst who wrote the report. “And looking beyond that must start now.”