HELICOPTERS DO crash, especially in bad weather, and the weekend crash that killed John Garang, the longtime leader of Sudan's southern rebels, does not appear to have been the result of foul play. The helicopter in which Mr. Garang was flying belonged to an ally, Ugandan President Yoweri Museveni ally; it was flying over territory controlled by Mr. Garang's own Sudan People's Liberation Movement. Even so, the suspicion of foul play has triggered violent urban protests that could unravel Sudan's fragile north-south peace accord. By Wednesday more than 100 people had died in riots in the capital, Khartoum. In the southern town of Juba, rioters attacked shops and homes owned by ethnic Arabs associated with the northern government. At least 13 people have died.

The challenge now -- both for Sudan's leaders and for the United States and other outsiders -- is to keep the north-south peace process moving in the hope that this violence will die down. So far, all parties appear to be responding as they ought to. The Bush administration immediately dispatched two senior State Department officials to the country. Sudan's president promised a joint north-south commission to investigate the causes of the helicopter crash and appealed for calm. Most promisingly of all, the southern liberation movement has appointed a new leader to succeed Mr. Garang without tearing itself into factions and has urged restraint from its followers. "It is just my husband who has died. His vision is alive," Mr. Garang's widow, Rebecca, told Reuters, alluding to his aspiration for a united and peaceful Sudan in which non-Arabs enjoy full rights.

African rebel movements, and indeed many African governments, are often led by strongmen who carry more on their shoulders than any individual should. Mr. Garang fit this mold: He made decisions without consulting colleagues; he did little to build political institutions in the areas of the south that he controlled or within his own movement; he was happy to embody the political aspirations of Sudan's non-Arab peoples. This ill-fated approach excluded orderly preparation for a succession and may leave other leaders without the stature necessary to persuade ordinary citizens to trust in a peace deal with the hated government. If that proves to be the case, then Sudan's north-south war may resume, dashing all hopes of using north-south reconciliation as the basis for peace in the western region of Darfur, where the government has committed genocide. But, in the speed and smoothness of his emergence as the new southern leader, Salva Kiir Mayardit holds out the hope that he can fill Mr. Garang's shoes ably. The Bush administration and its allies should encourage and support him. After decades of civil war and millions of casualties, Sudan has suffered more than enough.