From dawn until dusk, they walked the red-earth path between territory controlled by the government of Sudan to that held by the rebels -- small groups of men in jalabiyas, women in colorful clothes, and children on donkeys or their fathers’ shoulders or in baskets on their mothers’ backs. They carried jerricans that were filled with water at the start but were now dry, goats too young to walk, utensils, and weapons -- from nineteenth-century swords to rocket-propelled grenade launchers, sometimes both on one shoulder. Among the civilians walked rebel soldiers who were there to protect against depredation by government militias. The travelers' villages in the Ingessana Hills were four days back down the road and surrounded by government forces. Occasionally, a rebel car would come to pick up stragglers and drive them to the next resting spot. But the very weakest -- the oldest, the blind, those too sick to recover -- were left behind. The survivors pressed on toward El Fuj, a crossing point at the border between their war-torn homeland, the Blue Nile state in Sudan, and the new nation of South Sudan. It was one or two days farther on.

Sudan’s civil war has often been called Africa’s longest conflict. Its first stage, between 1963 and 1972, pitted rebels from the southern part of Sudan against the central government, which was dominated by a northern Arabized elite. The North granted the South a degree of autonomy in 1972, but it was not enough to paper over years of resentment. The conflict resumed in 1983, with the creation of the Sudan People's Liberation Movement/Army (SPLM/A). Although the movement had “liberation” in its title, its leader, John Garang, a charismatic southerner, advocated “diversity in unity” rather than the South’s separation. Less appealing in the deeper south, this relatively modest agenda was popular within border regions on the northern side of the eventual Sudan–South Sudan border, including Blue Nile state and the Nuba Mountains of South Kordofan.

In 2005, after 20 years of a brutal war, Khartoum and the rebels signed a peace agreement that granted the South (but not Blue Nile or South Kordofan) the right to self-determination. By 2011, most southerners had lost faith in unity and voted for independence. North of the new 1,250-mile border between North and South Sudan, some of the South Kordofan and Blue Nile rebels, now calling themselves the Sudan People’s Liberation Movement-North (SPLM-N), vowed to fight on. In June 2011, just after losing local elections and with one month to go before South Sudan’s independence, they once again picked up their guns and war resumed, first in South Kordofan then in Blue Nile. Since then, nearly 200,000 Sudanese civilians have made their way across the border to refugee camps in South Sudan.

For many of them, the idea that they are even crossing a border is a foreign notion. The placement of the new border was supposed to be based on provincial boundaries that existed in 1956, the year of Sudan’s independence. But those boundaries had never stopped moving before or since -- sometimes for good reason, such as facilitating the movements of nomads or access to a watercourse. Suddenly transformed into a solid border, though, the 1956 line looks rather arbitrary. Traveling along it, one mostly meets minorities afraid of being more marginalized than ever in what remains of Sudan and nomads scared of losing their grazing rights in South Sudan. As a result, African Union mediators have insisted that the new line become a “soft border,” one that gives rights to people on both sides of the fence: freedom of movement, trade, residence, farming and grazing, or even the right to vote and of dual citizenship. That idea is appealing, but making it work will require much more from both Khartoum and Juba than the current chronic low-grade warfare.

ALONG THE BLUE NILE

One afternoon in the dry season, I visited Chali, the main village of the Uduk tribe in Blue Nile. By an accident of history, the region was home to some of Sudan’s Christians, converted by American missionaries expelled from Ethiopia by Benito Mussolini in the late 1930s. By the time I got there, the village was largely deserted. The day before, government planes had dropped four bombs, damaging an empty hospital. Tree limbs were still smoking on the blackened soil around the nearby mosque. Built in 1983 with Saudi funding, the beautiful, castlelike brick construction had prompted many Uduk to join the southern, largely Christian, rebellion against Khartoum that was just getting started.

“The mosque is the cause of our problems,” Polis Macha, a local rebel, told me. “We understood they wanted to change our children to Muslims.” He was sitting with his gun in the church -- intact, but abandoned -- next door to the mosque. Martin Luin, the only one of seven priests who did not leave for refugee camps in South Sudan, was by his side. The Uduk fear that they have no place in a northern Sudan, whose ruling elite, Macha and Luin explained, is increasingly bent on asserting its Muslim and Arab identity. Before South Sudan’s secession, Sudan’s president, Omar al-Bashir, had warned that, should the South obtain independence, there would be “no time to speak of cultural and ethnic diversity.” In the North, he said, “Sharia and Islam will be the main source for the constitution, Islam the official religion, and Arabic the official language.”

The reason for the warning was obvious: After losing a third of its territory (and three quarters of its oil resources), Khartoum would not be ready for further accommodation. Bashir’s threats sparked considerable anxiety not only among Sudan’s few remaining Christians but also millions of non-Arab Muslims, many of whom live in war-torn regions along the border.

SEND YOUR CAMELS

One main reason for the deadlock over disputed parts of the border regions is that the governments in Khartoum and Juba are both fragile and wary of turning border people into rebels. An important site in their game is the so-called Mile 14, a territory that was the subject of thorny negotiations in 2012.

In the dry season, Mile 14, which spans 14 miles from north to south and 125 miles east to west, is a mostly empty plain inhabited by sedentary Dinka cattle herders but also grazed by Arab nomads from the North. I drove across the yellow grass until I reached the river the Arabs call Bahr al-Arab, the “river of the Arabs,” and that the Dinka call Kiir. The snaking waterway, edged with lush greenery, is the northernmost permanent watercourse west of the Nile. The steel hulk of a bridge linking both banks still served as a crossing point for northern traders and nomads in spite of the three southern tanks pointing their guns northward. The tanks are an artifact of South Sudan’s late 2010 strategy of arming that disputed part of the border.

When the Rizeigat Arabs, who live in the North, asked Khartoum to respond to what they saw as an invasion of their homeland by southern tanks, they were told to send their camels and armed herdsmen. The command might sound dismissive, but its message was clear: Get ready to “make a war,” as one Arab leader told me. Since then, tensions have intensified, with Rizeigat militias sometimes fighting against forces from South Sudan. The multiplication of cross-border incidents prompted another round of peacemaking between Juba and Khartoum, which, in September 2012, agreed to demilitarize the borderlands, including the whole of Mile 14. After months of dragging its feet, the southern army began to evacuate the disputed zone in March 2013. According to the United Nations, the troops soon came back.

Both sides know that the area will never be demilitarized. Repeated commitments by Juba to stop harboring northern rebels are unlikely to satisfy Khartoum or end rebellions in Sudan. With South Sudanese authorities not fully willing or able to prevent SPLM-N and allied Darfur factions from going back and forth across the new border, Sudanese rebels are at home in the borderlands. They claim to control 40 percent of the invisible line.

Another reason both Khartoum and Juba hesitate to make too many concessions on the border is that both are rightly worried about turning disgruntled people from the borderlands into rebels. As much as the Dinka from the border areas were the vanguard of the SPLM/A during the civil war, Arab tribes such as the Rizeigat formed the bulk of the paramilitary forces used by Khartoum to fight the rebels in South Sudan and later in Darfur. Increasingly feeling they were both manipulated and not adequately rewarded, Arab fighters joined the SPLM/A (several hundred are reportedly still in South Sudanese ranks). Some have now turned up among the northern rebel groups as well.

THE UNITY APPEAL

It is easy to find anti-Khartoum rebels in the ill-named South Sudanese state of Unity, which borders South Kordofan. The oil-rich province was supposed to symbolize the coexistence of the North and South, but that was a pipe dream. One day, after landing on a plain blackened by bushfires and dotted with oil installations, I drove north toward Unity State’s Jaw area in a vehicle bearing southern license plates but full of northern fighters. They had been caught unprepared by the South’s separation. They had not been into the North for years. At this point, none of them were sure whether they were now southern soldiers or northern rebels.

We reached a checkpoint along the border between Sudan and South Sudan. My guide, a northern rebel, was afraid that the southern soldiers manning the post would climb aboard for the sake of a free lift. “I don’t like them,” he said. “They’re undisciplined. They’re the guys who looted Heglig, for their own profit.” Some 30 miles away, Heglig, an oilfield in Sudan that is still claimed by South Sudan, had been raided by a coalition of the South’s army and northern rebels in April 2012. The same had happened in Jaw in February. Since then, southern and northern combatants were living in nearby camps and bathing together in Lake Jaw. My guide was more at ease at a second checkpoint, a few hundred feet on and intended to mark the northern side of the border, although it was not guarded by Sudanese soldiers but by rebels. My guide hugged them -- he was now at home.

For rebels in North Sudan, discussing the border is often painful. People from all sides and all tribes in Sudan resent the separation of the south, seeing it as representing a collective failure to accommodate southerners and “make unity attractive” -- a major promise of the 2005 peace agreement. The government in Khartoum and many in the opposition are not ready to lose any other part of their territory. A rebel from the Misseriya Arab tribe told me that he had no doubt that Heglig, his tribal homeland, was part of the north. But he also said disputed areas such as Heglig or nearby Abyei -- a flashpoint between North and South Sudan -- are supposed to be common to Dinka and Arabs, “who should live there in harmony.”

Our talk was interrupted by a northern Antonov plane, which circled us before dropping eight bombs not far from the road (and supply line) linking South Sudan and the rebel stronghold in the Nuba Mountains nearby, on the northern side of the border. But both the bombs and the Arab rebel suggested the same message: For the border to be peaceful it would need to be soft, as the African Union has insisted. Further talks on how to make it so would have to involve the governments in Khartoum and Juba, northern rebels, and the local people. Why couldn't a Dinka be a Sudanese citizen and an Arab a South Sudanese? The border might have to be weak in order to survive at all.

SHUTTERED PEACE MARKETS

Even at the height of the conflict that led to the division of Sudan, peaceful exchanges between border communities never ceased. Throughout the war, Arab nomads such as the Misseriya secretly traded with the rebels in both the south and the north. Some of those suq-al-salam (“peace markets”) still survive today -- but barely.

One northern trader, Yahya Mohammed, explained: “We Arabs want to establish good relations to bring our livestock to rebel areas and to South Sudan. So both sides meet in green areas at the border, and their livestock graze together without any problem. We also trade with each other. We used to call the markets suq al-salam, but we prefer suq sambuk.” A sambuk is a small boat migrants use to cross the Red Sea. “Going to these markets is just like navigating a sambuk: You don’t know whether you’ll come back or not. Two months ago, I brought fuel to the market, but government soldiers shot at me and left me for dead. The rebels rescued me.” In April 2012, Sudanese Vice President Ali Osman Taha declared the whole border area “an emergency zone.” He gave orders to the armed forces to shoot anyone smuggling across the border or the frontline with SPLM-N rebels. Yahya told me that when he heard the “shoot to kill” order, he decided not to go back to the government-controlled area.

It is impossible to build a durable peace between Sudan and South Sudan, and within both countries, through separate piecemeal fixes. By their own acknowledgement, international players, in particular African Union mediators, have focused on the relations between Sudan and South Sudan. After having tried everything possible to prevent or solve new conflicts between the two countries, they increasingly realize that peace will remain fragile as long as both governments remain undermined by internal divisions and conflicts with rebels. Both states should work to re-establish trust with their citizens, in particular in the borderlands. Border communities are aware that they matter; their lands are among the most populated, and their livestock, water, oil, and cross-border trade make them some of the wealthiest people in either country. Nevertheless, they feel abandoned by their governments. In Sudan in particular, an inclusive national dialogue could lead to their empowerment. Recent unrest in Khartoum itself makes this solution more and more popular among Sudanese from all sides and among international players.

Back in war-torn Blue Nile, at the triple border of Sudan, South Sudan, and Ethiopia, a local tribal chief, Uweisa Madi Zima, told me, “We’re not educated people and don’t understand much about politics. But the government that will treat us well will be our father, be it South or North Sudan.”