lone mountain towers over the countless shacks of Darfur’s largest refugee camp. This rocky summit, rising abruptly from an endless African plain, offers a view of breathtaking grandeur.

Open grassland unfolds in every direction, dipping into winding valleys with rushing rivers and groves of trees and dissolving into a horizon crowned with mountains.

The landscape has turned a verdant green under Sudan’s summer rains and, for a moment, an onlooker might forget that 75,000 desperate refugees are clustered below in Mornei camp. For Darfur has become a luscious, fertile wasteland.

Every glimpse of its scenery recalls the line from Bishop Reginald Heber’s hymn: “Every prospect pleases, and only man is vile.”

The vileness of man is everywhere apparent around Mornei. This region was once known as the “Dar Masalit” – the land of the Masalit tribe. Today, gunmen from the pro-regime Janjaweed militia have destroyed almost every Masalit village, killing thousands and forcing the survivors to flee into squalid camps.

The fields are green, but they are also empty of crops for November’s harvest. Darfur’s 1.2 million refugees – and another 158,000 in neighboring Chad – have been reduced to dependence on international food aid for the next two years at least.

The question that Darfur’s bewildered refugees find impossible to answer is: “Why has this happened to you?” The question that stumps the rest of the world is: “What is to be done?”

To begin with the “why,” few human disasters are more complex than Darfur’s and the first step is to squash a persistent myth. This is not a simple ethnic war pitting Arabs against Africans.

Generations of intermarriage and migration have made these labels almost meaningless. Almost all of Darfur’s 6 million people are of mixed race and the region’s tribes use Arabic as a lingua franca.

Instead, the conflict rages along two key divides. Underlying everything is rivalry between nomadic and settled tribes. The came land cattle-herding tribes from the north, mainly the Beni Hussein and Beni Halba, move with the rains and they come south every year in search of fresh pasture.

This brings them on to the lands of the Fur, Masalit and Zaghawa – the largest sedentary tribes. Clashes over land and water have often erupted and Sudan’s regime likes to argue that today’s fighting is nothing but a continuation of this dispute.

This claim is spurious, for conflicts over land and water were once settled amicably. Darfur enjoyed four decades of peace under British rule from 1916. Colonial officials averted clashes by acting as neutral arbiters, backed by a legal system. Tribal leaders also had their own ways of settling disputes without bloodshed.

Sudan’s current regime committed one of its greatest crimes by systematically destroying these ways of bringing peace. Instead of holding the ring as an honest broker, as the British had done, Khartoum deliberately upset Darfur’s delicate balance by constantly favoring nomadic over settled tribes.

Like any dictatorship, Sudan’s Arab-dominated military regime has only one overriding purpose – to hold power at any stake. Devoid of democratic legitimacy, and facing the long running rebellion in southern Sudan, it has always felt threatened. Nothing is more dangerous than an insecure dictatorship. Khartoum saw the nomads of Darfur as allies, solely because they were more “Arabized” than the settled tribes. Any African leader who dabbles in ethnic politics risks igniting a conflagration.

Yet this is exactly what President Omar al-Bashir chose to do. In 1994, he redrew Darfur’s administrative boundaries, arbitrarily creating the provinces of Northern, Western and Southern Darfur. This handed all the key positions of power to the nomadic tribes.

At a stroke, the settled tribes found themselves without any protection from the authorities. On the contrary, the regime encouraged the nomads to move south early and occupy huge swaths of their land. Serious clashes erupted in 1998 and 1999, in which hundreds died and scores of villages were destroyed.

When this fighting broke out, Sudan’s army did not attempt to restore order – instead, it intervened on the side of its tribal allies. The sedentary tribes were left defenseless.

A full-scale rebellion was the predictable outcome. Darfur’s insurgency began last February when rebels, styling themselves the Sudan Liberation Army, carried out a series of attacks. They managed a “spectacular” when they raided the airport in El Fasher, the largest city in Darfur, and killed hundreds of soldiers.

Mr. al-Bashir feared for the survival of his regime and decided on a Draconian response. He began arming the tribes he saw as his friends and encouraging them to pillage his enemies. As a deliberate act of policy, a second key division was introduced in Darfur – the separation between tribes seen as regime allies versus those viewed as enemies.

This turned Darfur into today’s charnel house. African fought African and, occasionally, Arab fought Arab. The black, settled Zaghawa people were written off as rebels and pitted against the black, settled Gimr tribe. The Masalit and the Fur were seen as the principal enemies.

Meanwhile, the “Arabized” Beni Hussein and Beni Halba were given guns, cash, and carte blanche to destroy the villages of their enemies and seize their lands. They became the mainstay of the Janjaweed, which translates as “demons on horseback.” As a deliberate act of policy, Darfur was transformed into a cauldron of conflict.

Against this background, the international community must do more than send aid and endlessly debate the dispatch of peacekeepers. Instead, Mr.al-Bashir’s regime must be told to end the dangerous practice of favoring one tribe over another and, in particular, to reverse the disastrous administrative reforms of 1994. That is one specific demand that the foreign secretary, Jack Straw, could make during his visit to Sudan.

Darfur’s people are not genetically programmed to kill one another. Amoral politicians in Khartoum have created this terrible war – and the world should demand an end to their wicked ethnic politics of divide and misrule.