. >> reporter: the town of bentiu lies in the heart of sudan in a state named unity; nothing could be farther from the mood here. in the local stadium, a graduation ceremony yesterday for the new police class quickly turned into a rally for separation. ♪ no one doubts that the mostly black african south sudan will vote to secede from a nation long dominated by the arabic- speaking north. the two sides have been mired in decades of civil war. it ended with a peace treaty in 2005, which called for the secession vote and negotiations to share revenues from the oil fields. although they are located mostly in the south, oil revenues have flowed to the north. if the peace treaty holds, bentiu will be just inside the northern border of the new republic of south sudan. it's one reason the town has been overwhelmed by thousands of returning southerners, people who had migrated to the more prosperous north in recent years. it's difficult to say exactly how many people have returned to bentiu and unity state, but the estimate of 100,000 is not exaggerated, according to relief agencies. that's al