At the last minute, al Bashir concedes to a divided Sudan

Omar Mr al Bashir has to struggle to stay on top of the factions. It is clear that he has had enough of international isolation, and no doubt thinks that the new state in southern Sudan will be dependent on Khartoum.

On Tuesday, the president of Sudan, Omar al Bashir, went to the south of the country just days before it votes in a referendum which is almost certain to see Sudan divided in two. Mr al Bashir has fought hard for years to hold the country together against the demands of southern secessionists.

Yet there was the president in Juba, wearing a southerner's blue robe over his suit, giving his blessing to the southern leadership's ambition to form what is likely to be the 193rd member of the United Nations. He said he would be "personally sad" if the country split in two, but he added: "We cannot deny the desire and the choice of the people of the south. This is their right."

There was no dancing and no smiles, but the message seemed clear. The soldier who overthrew the government of Sadiq al Mahdi in 1989 in order to stop it signing a peace deal with the south seems to have come to terms with the break-up of his country.

All indications are that the vote, which begins on Sunday, will be firmly in favour of independence, though the enormous difficulties of registering and counting votes in an area with almost no roads may lead the referendum to be fatally contested.

What is clear so far is that the referendum itself marks a rare success for Washington diplomacy, and that the world's view of Mr al Bashir might need to be reconsidered.

In the US, he is often in the top three in media lists of the world's worst dictators. This is strange and unjustified given that both he and his National Congress Party took part in contested elections last year. What is even stranger is that the US has chosen to engage with Mr al Bashir despite the fact that he stands indicted for war crimes and genocide by the International Criminal Court in the Hague for his suppression of the Darfur rebellion, in the west of the country.

This indictment puts him in a minority of one: he is the only serving head of state to have been so charged. His country is under US sanctions. Yet rather than seeking to arrest him, Washington has appointed a special envoy in the form of Scott Gration, who has offered Mr al Bashir the chance to emerge from isolation if the referendum in the south goes ahead. Mr Gration is regularly vilified as Khartoum's dupe by the Hollywood-led constituency in the US, which champions the rights of the southern Sudanese and the Darfuris.

What is even more surprising is that the usual motive advanced for US diplomacy - the need to get control of oil resources - does not apply to Sudan. Its oil is exploited by Chinese interests and, to a lesser extent, the French. France, however, has supported bringing Mr al Bashir to trial, when the traditional wisdom would have it supporting the president.

All this is so opaque that it is tempting to see the referendum in the simplest terms: as part of a US conspiracy to foment ethnic and religious dissent in order to slice up the Arab world. This theory has gained currency because the borders of the Arab homeland are clearly fraying.

The Kurds of northern Iraq are slowly drifting away from Baghdad, even though nominally they are still Iraqis. The allegiance of Iraq to Arab causes, following the US invasion, is now in question given that Iran looks set to be the strongest influence in Baghdad.

In Palestine, President Barack Obama has abandoned his principled rejection of Jewish settlements, allowing Israel to encroach ever further onto Arab land. And now a part of Sudan the size of Germany and France - and containing most of the country's oil reserves - is to be lopped off, leaving the Arab orbit for east Africa. The unifying factor here is that the impetus came from the US.

This analysis is superficially pleasing. But it does not address the realities of Sudan or why Mr al Bashir seems ready to divorce the south.

Sudan - the largest country in Africa - is literally ungovernable. Just holding together the northern part - which is mainly Muslim and Arab - tests the political skills of a Machiavelli. To unite the north with the south - populated by more than 60 different tribes following Christianity or African religions - would be the task of many generations. In fact, the south has known little but war since independence in 1956.

Sudanese leaders have a tradition of trying everything in their attempts to hold the country together. Gaafar Nimeiri, who took power in a military coup in 1969, went from communist, to Arab nationalist to Islamist.

Mr al Bashir began as an Islamist dictator but has gradually become a man that Washington can do business with. He has sidelined, jailed and then released Hassan al Turabi, the Islamist political leader, expelled Osama bin Laden at America's request, and held contested elections.

We know little of what goes on inside the National Congress Party. It is clear that neither Khartoum nor the southern leader, the Stetson-wearing Salva Kiir, want a new outbreak of war at the moment. It seems the referendum will go ahead more peacefully than predicted.

Does the president have a grand plan? All the history of Sudan suggests that leaders struggle to stay on top of their rivals and to contain the tribal and ethnic tensions of this vast country. A small mutiny or tribal rebellion leads to over reaction from the centre, which leads in turn to civil war.

Mr al Bashir has to struggle to stay on top of the factions in Khartoum. It is clear that he has had enough of international isolation, and no doubt thinks that the new state in southern Sudan will be so dependent on Khartoum - not least for the export of oil through pipelines to the Red Sea - that its soon-to-be proclaimed statehood will be severely limited.

Only a fool would predict a velvet divorce as happened when the Czechs separated from the Slovaks in 1993. There is bound to be more fighting at some stage. But so far, things are going more smoothly than anyone would have guessed.