Days away from the birth of the world’s newest nation, nearly every dusty street here has a splash of flags — raised on high poles over ramshackle huts, tacked to the front of motorbuses, painted red, black, green and blue on whitewashed walls. In the public square, soon-to-be citizens practice their newly composed national anthem, accompanied by a brass band. Children in green and blue school uniforms march along the main road singing patriotic songs.

But the train station near the center of Aweil provides a reminder that South Sudan’s independence is also a bitter divorce. A group of refugees sits beside the rails, surrounded by cooking pots and farm implements, their former lives carried in burlap bags. They are southerners — black and Christian or animist — who had lived in the Muslim, Arabized north.

An elderly man, Deng Deng Arop, tells me that their Arab neighbors had pressured them to leave. “They said, ‘You have to go to your own country. If you don’t go to the south, you will see what happens to you.’ ” Long lines of southerners waited to board trains. “They wanted to keep our sons by force,” says Deng, who reports that an official in charge of the refugees had prevented it. Passing through Kordofan, the southerners were given a final goodbye. Arab raiders ambushed the train, stealing grain and cash. Following the attack, Deng counted 20 dead. A 14-year-old boy, Bol Mayen Bol, was traveling with his older brother, Chan. In the chaos of leaving the north, his mother had gone ahead on an earlier train. During the ambush, Chan fled the train to hide and is now presumed dead. Bol shows blank shock rather than grief.

Sudan’s north and south have been at war, nearly without respite, since 1955 — imagine America’s Civil War lasting half a century. Millions have died from fighting and famine. This area of Northern Bahr el Ghazal was subject to frequent raids to capture slaves — many of whom are still held in captivity by northern tribes. Armed conflict continues along the border. Elements of the southern Sudan People’s Liberation Army (SPLA) are fighting in the Nuba Mountains and Abyei, where northern forces (as is their habit) employ violence and terror bombing against civilians.

And yet the ruler of northern Sudan, Omar al-Bashir — under indictment by the International Criminal Court — is scheduled to speak at South Sudan’s independence celebration. If he comes, it would show a boldness on Bashir’s part. It would also demonstrate the Sudanese paradox of deep hatreds and unavoidable ties.

Bashir was forced into the acceptance of southern independence. But he is a survivor who knows how to turn reverses into advantage. He can credibly tell his domestic audience that he is wringing major concessions out of the south — including a preferential oil deal — while expelling resented southerners from the north. And the United States is dangling some prospective benefits if Bashir allows a clean break with the south — perhaps the easing of sanctions and the removal of Sudan from the list of state sponsors of terrorism.

By inviting Bashir to the independence celebration, South Sudan’s government is making its own calculation. The north may be hated, but it remains the south’s primary trading partner. Sixty percent of food consumed in South Sudan is either produced in or transported across the north. Though the south produces oil, it imports refined fuel from its northern neighbor. The recent closing of the border due to fighting in Abyei has caused fuel shortages in this area.

The current, uncomfortable accommodation between north and south is fragile. Military skirmishes are inevitable along the undemarcated border. A number of southern commanders and political figures have family roots in disputed Abyei. SPLA forces in the region may not be fully controlled by the central government. And a more concerted fight for Abyei would be broadly popular in the south, where many view Abyei as stolen land.

Some southern commanders seem drawn to a strategy of keeping the north occupied and distracted with smaller-scale military actions. Some in the north seem equally intent on supporting anti-government militias within the south to weaken the new state. So far, South Sudan’s president, Salva Kiir, has skillfully de-escalated the situation. But it would be an easy slide from a border conflict to a general war — with a new flag carried into battle and new victims of a war that pauses but does not end.