The origin of tensions in Sudan is so geographic, so stark, you could see it even from the surface of the moon. The broad ivory of the Sahara in Africa's north set against the green savanna and jungles of the continent's narrowing center. A great, grass-stained tusk. Populations generally fall to one side or the other of that vegetative divide. Which side, north or south, largely defines the culture—religion, music, dress, language—of the people there. Sudan straddles that line to include arid desert in its north and grasslands and tropical rain forests in its south, and the estranged cultures on either side.
In Sudan, Arabs and black Africans had met with a clash. Islamic conquerors in the seventh century discovered that many inhabitants of the land then called Nubia were already Christian. The Nubians fought them to a stalemate that lasted more than a millennium, until the Ottoman governor based in Cairo invaded, exploiting the land south of Egypt as a reservoir of ivory and humans. In 1820 he enslaved 30,000 people known as Sudan, which meant simply "blacks."
Eventually global distaste for slavery put the slave traders out of business. The Ottomans retreated in the early 1880s, and in 1899, after a brief period of independence for Sudan, the British took control, ruling its two halves as distinct regions. They couldn't garrison all of Sudan—it's a massive country, ten times as big as the United Kingdom—so they ruled from Khartoum and gave limited powers to tribal leaders in the provinces. Meanwhile, they encouraged Islam and Arabic in the north and Christianity and English in the south. Putting effort and resources into the north, they left the south to languish. The question all this raises is: Why? Why was a single Sudan created at all?
One reason, again, is geographic. As the Nile flows north toward Egypt, it binds the disparate cultures along its banks in a fitful, sometimes hateful, relationship. It defines trade, environment, even politics, linking the affairs of north and south. When the British ruled, they needed to control the Suez Canal at the Nile's mouth, because it linked Britain to the "jewel in the crown," India. That meant controlling the Nile, so no enemy could divert it.
When the British withdrew in the mid-1950s, there's little wonder the place fell into civil war. Southern rebels battled the northern government fiercely during the 1960s, and half a million people died before the two sides struck an agreement in 1972. Yet the pact only gave each side a chance to breathe deeply and rearm for what would be a much bloodier war.
During the lull between the two civil wars, the government in Khartoum joined Egypt to embark on a breathtaking project in the south. Where the Nile spreads across southern Sudan— that great tableland—it forms the Sudd, one of Africa's largest wetlands. And the river's annual floods rejuvenate grazing lands where southern tribes have long kept their cattle. The partners decided to build a 225-mile canal to shunt the river past the Sudd, due north to supply water-hungry Egypt. They brought in an eight-story digging machine, and tribesmen stood and watched as their pastures were ripped up.