A vote this week in southern Sudan will determine whether the region will become an independent nation or continue to be yoked to the north. The United States and China, as well as Sudan's neighbors, are watching the referendum closely.
The week-long vote will end on Sunday. Although the final tally will not be known for some time, it seems virtually certain that south Sudanese voters will opt for independence.
They have chafed under northern rule since Sudan gained independence in 1956. Their differences are sharp and often have led to violence. Northerners are mostly Muslims and Arabic-speakers, while southerners are mostly Christians.
The next question is whether the north would accept southern independence. That debate is complicated but also eased by two facts. Most of Sudan's oil, the country's most important asset, is found in the south.
But the south is landlocked. Absent new, expensive, and time-consuming construction of international pipelines, Sudan's oil still will have to be transported from the south across the north. This economic interdependence offers a strong basis for north-south cooperation.
Whether the north would accept southern independence also turns on past relations between the two regions. On the basis of size and military strength, the north could roll over the south. But a renewed war likely would be expensive, difficult, and full of casualties.
Since the north-south peace accord of 2005, southern Sudan has received much more world attention, which the referendum is enhancing. The north would have to think carefully about its situation in the world if it were to consider suppressing a newly independent south by military means.
Because of Sudan's bloody history, such analysis could be excessively optimistic. At the same time, there is reason to hope that the referendum, followed by south Sudan's independence, would go well.