A Sudanese man waves the regional flag of southern Sudan during a protest in the small town of Kauda in the South Kordofan state on January 15, 2011, calling for electoral reforms in the Nuba Mountains region.  Khaled Desouki / AFP / Getty Images  Deep in the Nuba Mountains of Sudan, by the light of a full moon, I am passed a glass of sugary tea  and the discussion of another civil war in the heart of Africa begins. My two hosts in the town of Dilling are commanders in a government-sponsored Arab paramilitary force that a decade ago carried out Darfur-style atrocities against their African neighbors in the surrounding mountains. For nine years, they have held a ceasefire. But now the coming secession of South Sudan has prompted fears of renewed ethnic conflict.  The reason? When the line is drawn across Sudan to create two new countries, the Nuba Mountains and the state of South Kordofan in which they lie will remain in the north. That has once again sharpened divisions between Sudan's Arab rulers, who armed Arab tribes during decades of north-south civil conflict, and the minority Nuba Africans, many of whom fought with the south. My Arab hosts are adamant: no war, ever again. "Nobody wants more fighting," says Ibrahim Yagoub Jabreel. "If the government asked us again, we would refuse." But later, my go-between, Juli Argouf Buda, 71, a Nuba African elder, pulls me aside. "They are not telling the truth," he says. "Most Arabs enjoy being the government's militias. They want our land. To kill a Nuba, for them, is not a crime." (See photos of Sudan going to the polls.)  The Nuba Mountains are a jagged fulcrum for a region that has long been delicately balanced between war and peace. To the north is North Africa, mostly Arab, mostly Muslim; to the south, sub-Saharan Africa, mostly African, mostly Christian. That division runs across the continent, along the southern edge of the Sahara, and regularly sparks conflict from Chad to Nigeria to Cote d'Ivoire. But in Sudan, this meeting of worlds has proved the most explosive: around 2 million people died in two wars between north and south that lasted between 1956 and 2005.  In July, Sudan will split in two after southern Sudanese overwhelmingly voted for independence in January  a key condition of an internationally brokered peace deal sealed in 2005. But instead of ushering in peace, secession could be opening several new fronts of war. In the south, the new government in Juba, whose leadership is dominated by the Dinka tribe, is battling an ever-growing number of rebellions rooted in other tribes, who say they suffer marginalization  since January, more than 1,000 people have died in the fighting. (See why the north began to protest after the secession vote.)  And in the north, the split has also ratcheted up tensions: most of Sudan's oil lies in the seceding south, and the country's partition has opened new rifts in the ruling party as to whether its divisive iron-fist tactics are the best way forward. So far, the hardliners seem to be winning. Meanwhile, large-scale agricultural schemes and desertification have pushed the nation's poor Arab nomads further south for pasture.  Many expect these new trends and the old local grievances to converge with toxic results around the South Kordofan state elections, scheduled to start on May 2. Those fears are heightened by the fact that the Khartoum government's candidate for governor is Ahmed Haroun, who was a key mobilizer in the government-declared jihad against Africans in the Nuba Mountains in the 1990s. Haroun's election rival, Abdulaziz al-Hilu of the southern-based Sudan People's Liberation Movement (SPLM), tells TIME: "The future is very grim." Indeed, recent signs are not encouraging. On April 13, Arab militiamen torched al-Hilu's home village, killing up to 29 people.  Outsiders rarely hear about the gathering storm in the Nuba Mountains, and for one good reason: the Sudanese government wants it that way. Refused official permission to travel to the area, I snuck in from Sudan's south. I found a place of bare boulder mountains, dusty open savannah and poverty: while Khartoum now boasts gleaming steel-and-glass skyscrapers, the Nuba Mountains mud-brick villages have changed little since Africans fleeing Egyptian conquerors first found refuge in these slopes centuries ago. The one modern intrusion: AK-47s, everywhere. (Watch the empowerment of the southern Sudanese as they voted for secession.)  Theoretically, Nuba's African tribes have reason for hope. After the May elections, whoever leads the new South Kordofan state government will be mandated to present its demands to the national government in Khartoum  which, for the Africans, would include peace, greater autonomy, and exemption from national Shari'a law.  But even if the African-backed SPLM wins the poll, Khartoum is unlikely to want to cede more power to other regions after accepting the departure of the south  particularly since South Kordofan is home to the north's remaining reserves of crude oil. Pessimists foresee a nightmare scenario: renewed full-scale war between north and south. Thousands of soldiers in the Sudan People's Liberation Army (SPLA), the armed wing of the SPLM, are from the Nuba Mountains. Should violence escalate in South Kordofan, many of them would expect to travel north to join the fight against Khartoum and its militias. Malaak Ayuen, the SPLA's head of information, says the south will not send Nuba soldiers into South Kordofan. But at the same time, he warns: "We won't disarm them."  For Al-Hilu, the SPLM's candidate for governor, anyone who thinks the Nuba soldiers will accept an extended exile in the new country to the south doesn't understand how the rugged, moonlit hills resonate in the hearts of those born here. "Anybody who tries to stop them is not a wise person," he says. "They must come back. This is their homeland."  See the world's most influential people in the 2011 TIME 100.  See TIME's 140 best Twitter feeds.
Tensions are already high between the Arabs and minority Africans of the Nuba Mountains region in Sudan's north. When the country splits, fears are that violence is sure to follow