This Saturday, the United Nations welcomes a new member.

The Republic of South Sudan, with a population around 12m, will become the 193rd country in the world when it severs ties with the rest of Sudan.

The new country was born out of war. Populated by mainly black African tribes, it suffered decades of systematic neglect and under-investment at the hands of successive regimes in Khartoum dominated by narrow Arab elites intent on amassing wealth and power in the centre. That approach provoked decades of civil war which ended just six years ago.

Nevertheless, during Saturday’s celebrations in the southern capital Juba, Omar al-Bashir, the Sudanese president, and his old nemesis Salva Kiir, the president of new South Sudan, are due to smile for the cameras.

But it will be a sticking plaster image. Bashir has spent the last month making a show of his strength by ordering his armed forces to bomb men, women and children in South Kordofan. Though north of the border between the two countries, the black African population there has a history of sympathy with the south. There are credible reports of summary executions, often apparently on ethnic lines.

So the omens are inauspicious for this fragile new country, which already faces colossal development challenges. South Sudan is one of the world’s poorest countries. Most children do not go to school and the police force is poorly trained. There are worrying signs that rates of polio, measles and leprosy are rising.

Nevertheless, it has the potential to thrive, if only it had stability and good governance. Visiting last month with the Scottish charity SCIAF, I found it lush and green. Burgeoning crops of cassava and sorghum surrounded every village. There is no commercial farming or indeed any industry at all, but there could be.

People are seized with optimism about the future. The population clings to the hope that a new sense of South Sudanese patriotism will trump tribal differences, the government will tackle corruption, and education and healthcare will improve. “There will be no more suffering; people will be happy,” one farmer told me, expressing three decades of suppressed hopes. Yet on the eve of independence, he looks certain to be disappointed.

Since an interim government was set up in South Sudan in 2005, that new government – dominated by the former rebel army, the Sudan People’s Liberation Movement (SPLM) – has made scant progress in building the country’s desperately needed infrastructure, and not due to lack of money. South Sudan possesses lucrative oilfields and the 2005 peace deal provided for its oil revenues to be divided between north and south. However, a huge proportion of its oil billions has been spent on army wages and pensions.

There is already disquiet about corruption and a perceived ethnic bias in the government and army. This has fuelled internal conflict. The new government is fighting half a dozen militia groups.

So is South Sudan, as some would have it, “a pre-failed state”, destined to descend into chaos before it has even come into being? No; that is too harsh a judgment. The SPLM has sought to pay off rebels rather than address their grievances, but at least, in most of the country, there is peace. What’s more, the patchwork tribal groups making up the population are bound together, for now, by commitment to the new South Sudan. It is not yet a functioning democracy, but it still has a shot at becoming one.

What matters now is that the international community exert as much pressure as possible to end the horrendous violence in South Kordofan and bring about a fair and sustainable division of Sudan’s oil revenues. The country needs peace, a representative government and an end to the investment drought it has endured for so long. With money flowing out of the capital into the regions, leaving a bloom of schools, hospitals and roads in its wake, the people of South Sudan might just have the prosperous future they deserve.