From the grass stalls of Bentiu, where a burnt market and upended billboard bear scars of air strikes, South Sudan’s road north to Sudan buzzes with the locomotion of war. To the left and right, oil fields lie pocketed with shrapnel-filled craters. Civilians with chairs or beds on their heads stream south, as trucks full of South Sudanese soldiers and Darfur rebels rumble back and forth. Our convoy, escorted by the South Sudanese army, blows by the town of Lalop — emptied of civilians and teeming with soldiers, tanks, and anti-aircraft guns. Further ahead, we pull to a stop at a smaller encampment of grass huts and foxholes. Troops fan out to the east and west, bundled under trees, waiting. "They dropped 24 bombs on us last night,” said Brig. Gen. James Kuac, the commander. "Even ten minutes ago, they dropped four. It’s not good for you to stay long.”This is the latest front in one of Africa’s oldest wars, except this time the stage is much more prominent: after South Sudan won its independence last year, what was once a civil war has transformed into a full-blown regional conflict. Two miles north of this South Sudanese position is the de facto international border, where the fighting all began several weeks ago and spread northward as South Sudan marched on the disputed oil territory of Heglig, captured it, and then blitzed even deeper north, vowing to take more territory. South Sudan says it was acting out of self-defense, but who fired first is unknown. What is obvious is that tensions had been rising for months: South Sudan shut down its oil production to cut off the flow north, and talks between the two sides have been deadlocked. Meanwhile, Sudan angrily denounced South Sudan for its links to various rebellions across the border. South Sudan’s march north suddenly reversed when, on April 20, South Sudanese officials in the capital Juba announced their forces were pulling all the way back. Heglig was abandoned once again, its oil facilities ablaze, the town thoroughly looted.Now, the move is in Sudanese President Omar al-Bashir’s court, and he badly needs a victory to take home after being humiliated in Heglig by an enemy army that was a ragtag guerrilla force just six years ago. So far, Bashir has refused to return to talks and vowed to crush the South Sudanese "insects.” Meanwhile, South Sudan’s military is digging in to counter what they expect to be a retaliatory ground invasion, as Khartoum rains bombs from above, some killing civilians. South Sudanese and other security sources speculate that Bashir could try to capture the Unity oil fields, or even march all the way to Bentiu itself, before returning to the negotiating table with a better hand.South Sudan’s mobilization towards war has embarrassed the United States, which backed its quest for independence and continues to throw aid and diplomatic weight behind the young, fledgling nation. But South Sudan’s leaders say they have no apologies. "We liberated Heglig. Heglig is in South Sudan,” argued South Sudan’s vice president, Riek Machar, before boasting to TIME: "We are always the underdogs.” South Sudan hoped its withdrawal from Heglig will smooth over its friends’ ruffled feathers. But, that move failed to impress amid skepticism that the retreat was a strategic imperative and less a diplomatic concession. Facing a fierce Sudanese counter-offensive along a flat terrain with no natural defensive positions, South Sudan probably had little choice but to pull back.So, what now? Both armies are back to where they started, at the old border, but nothing is back to normal. The state of war rages on. South Sudan’s top military brass and field commanders continue to arrive at the front, as its troops ready for a big battle. Sudan launched several waves of ground attack on Sunday, but the attack was repulsed. Ever since, the front lines have sunken into an eery silence broken only by the sound of Sudanese war planes above and bombs below. The aerial attacks are not limited to the front lines: on Monday, in Bentiu, a car of journalists had just crossed the town’s bridge when a bomb fell nearby. Dirt basted into the air fifty yards away. One of the missiles hit the market, where a charred boy’s corpse lay twisted under billows of smoke.There is hope: the quieting front lines could be a sign that external diplomatic pressure is working. U.S. State Department spokesperson Victoria Nuland on Thursday called on the two parties to "formalize” the ceasefire, which she called a "small glimmer of hope.” China has deep energy interests in both nations and is pushing for an end to the fighting. The U.N. has strongly condemned Sudan’s aerial attacks, just as they denounced South Sudan’s capture of Heglig earlier. In a meeting in Ethiopia on Tuesday, the African Union passed a roadmap to peace with a three month ultimatum for both sides to strike a deal, or else. Diplomatic sources say both sides are being threatened with U.N.-backed sanctions if they don’t cooperate. With both economies spiraling downward, leverage may be limited. South Sudan, in particular, already has shut down its oil production and has no functional economy to blacklist. But, South Sudan, unlike its northern neighbor, still seems sensitive to international condemnation. "South Sudan can’t afford to be a pariah state,” said Vice President Machar.The grim reality on the ground that makes peace so elusive is that there is not just one conflict in the Sudans, but many — and they are all connected. Exhibit one: the out-of-place Darfuris, northern Sudanese who have joined up with South Sudan for the fight. Boasting roofless trucks and heavy machine guns, the Justice and Equality Movement rebel fighters roll like a modern calvary, excelling in hit-and-runs and flanking maneuvers. Just to the east of Heglig are the Nuba Mountains, where more South Sudan-aligned rebels, allied with JEM, have been putting up a spirited fight against Sudanese troops and taking ground. Their rebel partners further to the east, in Blue Nile, are waging guerrilla warfare on another front against Bashir. Until Sudan finds a way to accommodate its own marginalized opponents, and until South Sudan is willing to admit its links to them, real peace along the world’s newest border will likely remain a distant mirage on a road map to nowhere.

TIME