One of the two most prominent divides in Africa is the Great Rift Valley, the geological scar that runs north and south along the eastern half of the continent and has been forming over eons as the African tectonic plate slowly splits into two. The valley's connection with human history has been first and foremost as a cradle of mankind itself, about which modern humans have been able to learn something thanks to a pattern of sedimentation that has preserved and then revealed the bones of human ancestors. More recent human history in and around the valley, and specifically the portion of it along the eastern border of Congo, has been some of the bloodiest in modern times, with successive rounds of warfare beginning in the late 1990s causing more deaths than any other conflict since World War II.

The other great divide does not have a name, is not visible on physical maps of the continent, and runs east and west. It is the blurry boundary along the Sudanian Savanna where largely Muslim North Africa meets the areas to the south inhabited mostly by Christians and adherents of native religions. It is a civilizational and cultural fault line that has not only been the scene of much conflict but has also largely defined the conflicts. The line is not visible on political maps any more than physical ones, meaning that the conflicts have largely played out within countries as civil strife. Currently a major focus is the portion of the line that runs through Sudan, given the likelihood that, as Benny Morris recently discussed in these spaces, southern Sudanese will vote in a referendum next month to make that portion a political boundary and create a separate state.

But it is not just Sudan that is involved, given that this divide extends much farther to the west. Currently another hot spot along the line that is being racked by violence is Cote d'Ivoire, where an incumbent president from the south refuses to relinquish his office after a disputed election last month that most outside observers believe was won by his opponent from the north. Then there is the most populous country on the continent, Nigeria, whose political system has been a delicate balancing act between the Muslim north and a largely Christian south. One of the balancing mechanisms—an understanding that the presidency should alternate between northerners and southerners—was upset earlier this year when President Umaru Yar'Adua, a northerner, died in office. The vice president from the south who succeeded to the presidency, Goodluck Jonathan, has decided to press his luck by running for a full term in an election next year. This angers many northerners, who believe that because Yar'Adua did not complete a term the next elected president ought to be another northerner.

Such disagreements raise the question of whether the occupants of each side of the divide would be better off if, as the southern Sudanese seemed poised to do, they were to draw political boundaries along the divide and go their separate ways in separate countries. The main argument against doing so is that this could start a territorial unraveling whose end no one could predict. This is why African rulers, despite the cross-border trouble they have made for each other over the past half century, have generally lived by a tacit understanding that they should stick with the boundaries left by their former colonial masters, notwithstanding the non-congruence of those boundaries with ethnic and sectarian patterns of habitation. Formal political division would raise the sorts of practical problems that Morris discusses regarding Sudan. It might also lead to more extreme policies in the successor states, at the expense of any minorities that remain there. Sudanese strongman Omar al-Bashir has already declared that if the south secedes he will implement a more sweeping form of Sharia, while making Islam the only religion in the country and Arabic the only language.

An opposing argument is that African rulers have not had to wait for secession to take such exclusive or extreme measures. Islamization in Sudan, with all of the resentment it has caused among southerners, dates back more than a quarter century to the regime of Jafaar al-Nimeiri. I remember visiting Khartoum in 1983 shortly after Nimeiri had launched his Islamization campaign with a ceremony in which liquor and beer bottles were smashed along the banks of the Blue Nile. Along the river a couple of days later, there still was plenty of broken glass and a pervasive smell of alcohol for anyone who wanted to breath it in before the country went dry.

Moreover, the political cultures of the countries along the divide simply do not seem to have the capacity to bridge that divide. Political separation would largely remove the single biggest impediment to political comity and stability in several of the countries. To some extent separation would formalize what is in some places a de facto reality. Cote d'Ivoire has effectively been separated into northern and southern entities since a previous round of civil war that ended eight years ago.

There is no obvious and clear answer to the overall question about whether political separation along the divide would be desirable. In any event, no one is going to engineer a general solution to this problem—not the Africans themselves, and certainly not outsiders. The problem will be addressed in separate fits and starts, such as the Sudanese referendum. It will be interesting to observe not only the impact of that event in Sudan itself but also any demonstration effects it may have farther west along the divide.