More than any other continent, Africa is wracked by separatists. There are clearly defined liberation movements and other rudderless, murderous groups known for their cruelty or greed. But these rebels share at least one thing: they prey on weak states struggling to hold together disparate populations within boundaries drawn by 19th-century white colonialists.

The colonial history is a prime reason that Africa remains a continent of failed or failing states. But people in southern Sudan may be headed on a different path. On January 9, they began a monthlong vote on independence from the Sudanese government in Khartoum. If successful, South Sudan will become a rare exception in Africa - a state that is reorganizing its colonial-era borders. It might even set a precedent for others.

The situation in southern Sudan has already set off an agonizing debate, a half-century in coming, over the wisdom of trying to hold together the unwieldy colonial borders in the first place.

Even though many of those frontiers carelessly sliced through rivers, lakes, mountains and ethnic groups, few of the leaders who shepherded Africa to independence a half-century ago wanted to tinker, because redrawing the map could be endless and contested. So, on May 25, 1963, when the Organization of African Unity was formed in Addis Ababa, Ethiopia, it immediately recognized the colonial-era borders.

In hindsight, it is clear that the old boundaries often hurt prospects for state building. But back then, and even today for many Africans, the alternative of tiny ministates seemed even worse.

“In 1963, the O.A.U. did something very important: they sanctified the borders,” said Sadiq al-Mahdi, one of the grandfathers of Sudan’s politics, a vibrant man in his 70s. “But now this sanctification is gone. The borders have been polluted.

“And to resort to self-determination to solve your problems will break up Sudan, will break up Ethiopia, will break up Uganda, will break up all of Africa, because all African countries are made up of such heterogeneous elements.”

Mr. Mahdi was an architect of the most brutal phase of the north-south civil war in Sudan in the late 1980s, and is widely blamed for unleashing tribal militias against southern civilians, an accusation he denies.

Eventually, the southerners won. And he and northern Sudan are afraid. If the southern third of Sudan is lopped off, with it goes most of Sudan’s oil. Even though much of that oil still must flow through the north in pipelines for export, northern Sudan is in for a rough time.

But divorce will also be messy for the south. It’s not as if there is a knife-sharp cultural line where northern Sudan ends and the south begins. Many communities, like the Misseriya nomads, drift back and forth across that line to graze their animals, and the Misseriya are now refusing to be categorized as northern or southern.

Most Africa experts agree that there was considerable international pressure on the African Union, the successor to the Organization of African Unity, to make southern Sudan an exception to the rule about preserving old borders.

“Recognition is seen as a very, very bitter pill,” said William Reno, a political scientist at Northwestern University in Illinois. And Phil Clark, a lecturer in international politics at the School of Oriental and African Studies in London, said that until last year, “the A.U. mantra was that independence for the south would lead to further conflict.”

But the African Union, which needs the West to finance peacekeeping missions, yielded in the face of enormous American and European support for the southern Sudanese - support rooted in perceptions that southerners have long been Christian victims of Muslim persecutors.

There was also the matter of Sudan’s president, Omar Hassan al-Bashir, who was indicted by the International Criminal Court on genocide charges for atrocities in Darfur. He is also suspected of reviving old contacts with the brutal Lord’s Resistance Army in Uganda to destabilize southern Sudan.

“Could it be that Bashir’s support for the L.R.A. and other rebels has made countries exhausted” with him? wondered Maina Kiai, a Kenyan human rights advocate. “Or could it be self-interest among the neighbors hoping to cash in on a new, unformed state that has plenty of natural resources?

“I do think the oil could be a major factor,’’ he added, especially for Kenya, Uganda and perhaps Congo. (There has been talk of one day building a pipeline through Kenya and Uganda that could let the south’s oil exports bypass the north.)

Letting southern Sudan break free could also set a wide and unpredictable precedent - including for the Western Sahara, the Ogaden region in Ethiopia, the Cabinda enclave in Angola, and Congo.

There is also Somaliland, the only functioning part of Somalia; it recently held elections followed by a peaceful transfer of power.

Michael Clough, who directed the Africa program at the Council on Foreign Relations in the 1990s, said he thought that the African Union did not play the same influential role it once did. He expects that local balances of power, more than anything else, will determine whether a putative state like Somaliland actually becomes independent.

When the union was founded in the 1960s, “there were a number of strong and articulate African leaders,” he said. “Today, I just don’t think there are many leaders left in Africa who have political/moral authority.”

Maybe Africa is moving toward an understanding that smaller can be better - with colonial-era borders adjusted to carve out smaller, more governable units.

Mr. Clark doesn’t agree. “Africa doesn’t need a new map,” he said. “It needs new forms of leadership. In particular, it needs leaders who use national resources to benefit all citizens.”


By JEFFREY GETTLEMAN