As 2007 draws to a close, and with it the fifth year of war in Darfur, a seismic shift is taking place in Sudan's westernmost region. This emerging situation will determine the course of the conflict there more than any other single factor, except the collapse of the North-South peace agreement signed in January 2005. At the heart of this shift are the region's forgotten casualties of war - its Arabs.

To understand the importance of what is happening in Darfur today, rewind to October 2002 and the first big government-Janjaweed attack on the central Jebel Marra mountain, four months before the Darfur rebels declared themselves. Shartai Suliman Hassaballa, the longest-serving chief of the Fur tribe in Jebel Marra, remembers it well: "On 10 October 2002, the Janjaweed attacked Kidingeer and killed 30 civilians, including three of my brothers. They were led by Juma Dogolo of the Awlad Mansour tribe, an immoral, uneducated man who was nobody until the government gave him weapons."

Exactly five years later, in October this year, Juma Dogolo's nephew led the strongest Arab militia of South Darfur - arguably of all Darfur - out of an alliance with the government and into alliance with the rebels of Jebel Marra. With him he took brand-new vehicles, Thuraya telephones, heavy weapons and, reportedly, millions of dollars given him by the government as the price of participation in its latest offensive. Mohammad Hamdan Dogolo, "Hemeti," had been responsible for security around Nyala, the capital of South Darfur state, and the government was in no doubt about the importance of his mutiny: Three weeks ago, it unleashed the air force against him.

Arab militias - the so-called Janjaweed - are the lynchpin of the government's war in Darfur. Without them, the war would soon be over. The regular army is poorly motivated, poorly trained and demoralized by a series of crushing defeats. Its officer class dislikes the partnership with the Janjaweed and the abuses that have characterized it, for which the International Criminal Court (ICC) is now pressing charges.

When rebellion first broke out in Darfur, the government had no difficulty in raising Arab militias to fight. The camel-herding Abbala Arabs especially were some of the poorest and most vulnerable of Darfur's citizens, their herds decimated first by drought and then by raids by their Zaghawa neighbors, especially in the run-up to rebellion. But the war has destroyed the economy of Darfur and separated communities whose livelihoods were interdependent, to the detriment of Arabs and non-Arabs. As the firestorm of 2003-2004 abated and the war took on a life of its own, the government began to treat with contempt those who had answered its call to arms and were now demanding recompense. It was even whispered that Khartoum might hand some over to the ICC, to save its own skin.

When Hemeti mutinied, he cited the double betrayal of the Abbala Arabs: broken promises to provide their nomadic communities with health, veterinary services, schools and water, and unfulfilled commitments to pay militia salaries and give compensation for war dead. He said he took up arms against the rebels to defend his tribe after thousands of camels were stolen and scores of his relatives were abducted by Zaghawa rebels of the Sudan Liberation Army.

That was then. Today the Zaghawa SLA leader, Minni Minawi, is senior assistant to Sudanese President Omar Bashir, with power, on paper, to reform the Arab militias. Minawi was the only rebel leader to sign the stillborn Darfur Peace Agreement in May 2006.

Hemeti's mutiny was not the first - several less important militia leaders had already joined the Fur rebels of Abdel Wahid Mohammad al-Nur in Jebel Marra - but was easily the most significant. As the year ended, it appeared to be spreading to another Arab tribe, the Habbaniya, whose reason for taking up arms against the rebels was also the abusive behavior of Minawi's men.

One of the main challenges facing the Sudan government and the international community in 2008 will be how to respond to moves like Hemeti's. The government may be able to buy a measure of Arab support in the short term, but Darfur's Arabs are making clear that they are no longer willing to be Khartoum's cannon fodder and the Janjaweed drain seems likely to continue. The international community, too, has some hard choices to make. Hemeti may have committed war crimes and Abdel Wahid may be excessively difficult. But the Arab-Fur alliance is the most significant political and military development in Darfur since the war began. Yet the international community has never engaged the Arab militias and has subjected Abdel Wahid to a policy of neglect ever since he prioritized security in Darfur over renewed peace talks.

Abdel Wahid drives the international community to distraction. He is stubborn, difficult, moody and demanding. But he not only has the support of Darfur's Arabs; he has the endorsement of the overwhelming majority of the war-displaced, whose rejection of the Darfur Peace Agreement sealed its fate. Abdel Wahid rejected the agreement because he believed it lacked security guarantees. Since then he has focused on reconciliation with Janjaweed, to provide his own security guarantees. He told Hemeti: "The regime used you. It promised you many things and gave you nothing. We bear you no grudges. Your property and your people will be safe." Hemeti, he says, could not believe his ears. The government had told him: "You killed people and you will never be forgiven."

Dealing with the Abdel Wahid "problem" by neglecting him is no longer an option. Nor can the Arabs of Darfur continue to be excluded from peace efforts, on the grounds that the government speaks for them. It neither speaks for nor cares for them. If groups like Hemeti's are engaged, Abdel Wahid is re-engaged and North-South war is averted, there is a chance that Darfur may eventually find peace and stability. If not, the players will take new partners - and the dance of war will continue.

Julie Flint has written extensively on Sudan. She is the author, with Alex de Waal, of "Darfur: A Short History of a Long War." She wrote this commentary for THE DAILY STAR.