Southern Sudanese expatriates from across Europe voted in the independence referendum in London in January, a stone's throw from the Palace of Westminster. Hundreds of southern Sudanese travelled to the British capital to register and cast their votes. Every single voter I spoke with at the time said they intended to vote yes to separation and spoke optimistically of a better life in a new country.
But many of the Sudanese staff at the polling place could not vote because there were actually from the north, from what now remains of Sudan, and in private conversations shades of sadness and even bitterness could be heard. "Why," one asked, "are the southerners so ungrateful?"
That sense of sadness has been common as Arabs have watched Sudan's division, but in many ways South Sudan will remain part of the Arab world.
Such conversations point to the trauma of the long separation. Two civil wars have been fought and millions have lost their lives in the decades-long struggle for independence. Last weekend this long journey finally reached its destination.
Three days in and there is still jubilation in Juba, the new state's capital. But with the party over, the real work begins, and the facts about this newest of nations is sobering.
The bad news is very bad. The population is relatively small (perhaps eight million, compared to 30 million in Sudan, although no census has been carried out for decades), and has serious developmental challenges. Three-quarters of adults cannot read - and the United Nations estimates that figure rises to 92 per cent of women. Fifty per cent of South Sudanese live below the poverty line and more than that do not have access to clean drinking water.
Even compared with its northern neighbour, South Sudan is in an exceptionally parlous state. The headline figure often quoted is that the entire country - roughly the size of Texas - has only 100 miles of paved road.
Much of the good news relates to natural resources. Before the split, Sudan produced about 500,000 barrels of oil per day, and now South Sudan controls three-quarters of that. With outside help, South Sudan could build its own refineries, instead of relying on those in the north.
The south has a lot of fertile land that could be further developed. The UAE has already purchased 30,000 hectares on which to grow alfalfa; more land could be developed. That would be good not only for countries such as those in the Gulf, that don't grow sufficient food of their own, but also for neighbouring African countries like Ethiopia and Kenya, now suffering from a severe food crisis that may tip over into famine.
As well as being the world's newest country, South Sudan could be the latest country to join the Arab League. The league's deputy secretary general Ahmed Ben Helli has signalled the new state would be welcome to join. That should be a signal of intent for the Arab world.
As bad as it is and as good as it could be, it should be the Arab north and the broader Arab world that rebuild South Sudan, for the betterment of both.
The UAE has already begun. Two weeks ago South Sudan's vice president Riek Machar toured the UAE, meeting ministers and seeking investment. He suggested South Sudan's first embassy would be in Abu Dhabi, as a gateway to the region and to the wider Arab and Islamic world.
That would be a good move, a meeting of investment capital and investment potential. As one businessman said of South Sudan: "There is the potential in everything, from housing to roads to hospitals and schools."
It is not just the Arab world that should seek to aid South Sudan, the northern Sudanese should too. Sudan's president Omar Al Bashir - who fought a civil war to prevent secession - struck a conciliatory tone in his speech on Independence Day last weekend.
"We will fulfil our commitment to help the new state of South Sudan in its first steps, because we want it to succeed, and because its success will be our success," he said.
Those are good words and ought to be followed by bold action. The two countries need each other.
The conflict between north and south has long been framed as one between Arab Muslims and African Christians. The reality is more complex: both nations are a mix of ethnic groups and religions. The new country is a vast area with distinct regions and little sense of a collective identity as "South Sudanese". The civil war united them against a common enemy, but not among themselves. There continues to be open conflict between ethnic groups and political factions within the south.
The old Sudan was created out of the rubble of the borders the British had imposed, with successive governments in Khartoum attempting to keep the country "unified". In reality, they should have let the southerners secede; it would have been less costly for both sides, in blood and in treasure.
The Arabs and others of the north must accept their responsibility for maintaining a discriminatory system against southerners. But they must also find a way to move past it. Much of the discontent between north and south - and currently, among groups in South Sudan - has to do with inequitable distribution of resources. As tempting as it might be for every side to turn its back on the others, it will be easier if they work together to prosper together. Anything else risks that inequality sliding the region back towards war.
Feelings are raw, as they must be after so many decades. But despite the division of Sudan, the prospects for prosperity are real and tangible. Alongside the South Sudanese, the Arabs must play a role in building Africa's newest nation.
