There's Ayen, a woman from  Blacktown who now works in PR for a local oil company, banker Emmanuel, who studied finance at Macquarie University, and an engineer, David, who left Melbourne to take up a job as a government adviser. They tell me of doctors, soldiers and ambassadors who have returned to South Sudan after spending years in Australia.

William Agar Anyar, who once built beds at a factory in western Sydney, hopes to open a "Hotel Australia" in Juba. "I'm a proud Aussie," he says. "But I want to give something back to South Sudan." Akoc Manhiem, who has set up a foundation to promote peace and development, reckons several thousand South Sudanese-born Australians have returned since the new republic was created three years ago. "There is a huge number who have come back to give an example of what Australia has to offer: a vibrant, harmonious society," he says. "They are integrating themselves into every sector of the economy here."

Aussies have even infiltrated South Sudan's political class. Gatwech Lam Puoch lived in the Melbourne neighbourhood of Dandenong North between 2000 and 2007 before returning to South Sudan "to make a contribution and support my people". Gatwech, who honed his political skills in the Victorian Liberal Party, is one of two Australian citizens in South Sudan's national parliament. "I was probably the first South Sudanese to get involved in Australian politics," he says. Gatwech, from the ruling Sudan People's Liberation Movement, chairs South Sudan's parliamentary committee on energy and mining and wants to promote more Australian involvement in the country's oil sector.

Deputy Foreign Minister Peter Bashir Gbandi has six sons in Brisbane: "Three of them are in university and the fourth is about to go, so we are very grateful [to Australia]."

Manhiem says most returning members of the diaspora have traded life in Australia, one of the world's richest nations, for life in one of the poorest so they can make a difference in their fledgling homeland. "I was always thinking about what was happening in South Sudan," he says. "I did not find it easy to live in Australia when there are so many needs back in South Sudan."

There was dancing in the streets of Juba when South Sudan gained independence on July 9, 2011. The world map was redrawn that day when a portion of Sudan about the size of France was formally carved off to create the new republic. The historic separation followed two bloody civil wars that cost nearly three million lives and spanned five decades. A peace agreement signed in 2005 was followed by a plebiscite in which 98 per cent of South Sudanese voters opted for independence from Khartoum.

South Sudan's creation had received strong backing from the US administrations of both George W. Bush and Barack Obama. On the day South Sudan became a nation, Obama hailed it as a "step forward in Africa's long journey toward opportunity, democracy and justice" and a reminder that "after the darkness of war, the light of a new dawn is possible".

Sentiments like those helped draw home South Sudanese-born Australians, along with many others from the new nation's far-flung diaspora. But the lofty hopes are being sorely tested. Last December, the infant nation turned on itself after the country's president, Salva Kiir Mayardit, accused his deputy, Riek Machar, of plotting his overthrow. Machar denied the allegation, but marshalled a large force drawn from the army to fight the government.

The rebels now control a large chunk of the nation's east. About 10,000 people have been killed during the war and 1.5 million have been displaced, with the military conflict triggering a humanitarian emergency. Many farmers have abandoned their land to escape the fighting, making food scarce. Aid officials say nearly four million people are hungry and famine looms in parts of the country.

South Sudan sits on Africa's third-biggest oil reserve and has lucrative deposits of gold, copper, iron and diamonds. There's an abundance of arable land and rich water resources. But it's a country starting from scratch. Outside a few oil production enclaves, South Sudan's 11 million people live in a largely undeveloped, subsistence economy. The median age is just 18 years and about a third of the population is aged less than 10.

South Sudan's gross domestic product in 2013 was $US13.8 billion, or less than 1 per cent of Australia's. About 97 per cent of the government's revenue comes from one source - oil - and half a century of war has meant almost no investment in infrastructure. The extent of South Sudan's poverty is on show when I take a helicopter flight from Juba. Airborne over the White Nile, which runs the entire length of the country, the lack of bridges is striking. "The whole of South Sudan has only one bridge - the one that spans the Nile at Juba," Gatwech tells me later.

There were just 110 kilometres of paved roads in South Sudan when it gained independence. The transport networks are so bad that during the rainy season 60 per cent of the country is inaccessible by road. Three of South Sudan's 10 provincial capitals have no electricity generators.

The country's demography has made it vulnerable to ethnic division. The largest tribal group, the Dinka, make up about 15 per cent of the population and the next largest, the Nuer, about 10 per cent. Many from both tribes still bear the traditional facial scars of initiation: V-shaped markings on the forehead of the Dinkas and six horizontal lines on the foreheads of the Nuer.

There are dozens of other clan groups in South Sudan speaking a host of languages. Ancient clan rivalries were put aside during the long fight for independence from the ethnically Arab population to the north. But South Sudan's tribal fissures are now proving destructive in a nation awash with guns. The political stoush between President Kiir - a Dinka - and Machar - a Nuer - has split the nation along ethnic lines. A nation weary from decades of war is being racked by upheaval once more.

I meet many people in South Sudan with gut-wrenching stories of displacement and loss, but few more harrowing than John Garang's. In the early 1980s, at the age of 11, he was separated from his parents at the start of the Second Sudanese Civil War, which lasted 22 years. John fled his hometown of Bor in central South Sudan and joined a group of more than 20,000 children who trekked enormous distances seeking refuge from hunger and violence.

The group, which became known as Sudan's "Lost Boys", first walked to Ethiopia. But Garang almost didn't make it. "On the walk I got malaria," he says. "I became unconscious and was unable to move. I was lying down on the side of the road for a long time. But I decided I did not want to die there, so I managed to stand. By good luck, a guy appeared. He came behind me and caught me and put me on his shoulder. He carried me until we reached the border."

In 1991, the Lost Boys were forced to leave Ethiopia after the government there was overthrown. Garang tried to return home but fighting thwarted his plans. Like tens of thousands of others, he walked to Kenya instead. There Garang finished his schooling, trained to be a teacher, married and started a family. But life was difficult - his first-born child died in a Kenyan refugee camp. It wasn't until 2007, after the peace deal that ended Sudan's civil war, that Garang finally felt comfortable to return home. That year, he met his parents for the first time in two decades.

The kindness of the stranger who carried Garang to the border of Ethiopia when he was a boy has become an inspiration. "That man's help saved my life and I feel like I have to do the same for others," he says. "My heart is to help people so they can survive as I survived." So Garang has become an aid worker with non-government organisation Save the Children (which supported Good Weekend's trip).

But Garang's life-long story of displacement is not over. When fighting flared in his hometown of Bor last December, his wife, children and parents were forced to run for their lives. They have taken refuge in Uganda while Garang remains behind in his strife-torn homeland to work with displaced families. He is now based in Mingkaman, a ramshackle river town in central South Sudan where a whole new generation of uprooted families are taking shelter. More than 90,000 people have set up makeshift huts in the area, having fled Bor when rebel troops rampaged through the town.

Eleven-year-old Ngong saw six people shot, including one of his uncles. He submerged himself in the Nile River for more than two hours to hide from the gunmen. "I can still see those people lying down dead," he tells me. "I'm still in fear of attacks."

For many in Mingkaman, it's not the first time they have been displaced. Nyangker Awol was five when she and her mother fled fighting in Bor. They lived in a refugee camp in Kenya for 17 years before returning to their home town in 2008. Now with six children of her own, Awol has been forced to flee again. "I'm the one running with a daughter who is five this time," says the 29-year-old. "Will my child have to have the same experience as me and my mother? If I'd known it would end up like this, I would never have had children."

The failure of a series of ceasefire agreements brokered between the government and the rebels has discouraged tens of thousands of families across South Sudan and in neighbouring countries from returning home. Instead, their lives are in limbo and they depend on rations provided by the United Nations World Food Program.

When I visit, Mingkaman is captivated by the prospect of a traditional Dinka wrestling tournament. Herdsmen like Agutbul Mathieu have walked for hours from cattle camps to try their luck against the strongest men in the district. "I have drunk a lot of milk and I have thrown a lot of people recently," he tells me. "I made someone unconscious while I was practising yesterday. That's why I'm confident I'll do well."

The tribes of South Sudan are remarkably tall and Dinka wrestlers are a daunting sight - many of them stand well over two metres. As it turns out, the Saturday afternoon tournament is postponed by local authorities at the last minute, but that doesn't stop the thousands gathered throwing a party anyway. The throng of would-be champions and spectators spend hours singing, dancing and jumping instead of wrestling.

The next morning, more than 600 parishioners cram into Mingkaman's mud-walled St Paul's Episcopal Cathedral, where two drums lead the singing. The theme of the moving sermon by local reverend Daniel Makuel could not have been more poignant and appropriate: resilience in the face of suffering.

The humanitarian operations in South Sudan are the world's biggest, outstripping other high-profile emergencies in Syria, Iraq and Gaza. "This is a complex emergency," says aid worker Caitlin Brady. "We've got conflict, we've got constraints around the weather, we've got disease outbreaks."

Juba's small airport has become a hub for this vast humanitarian project. Because so many aid workers must be ferried around South Sudan, the UN's Humanitarian Air Service has set up a mini domestic airline to keep isolated towns across the country supplied and connected. Some routes can only be serviced by helicopters because rudimentary airstrips turn to mud in the rainy season, making it impossible for planes to land.

I take one of the UN helicopters, piloted by a Ukrainian crew, to the hard-hit, rebel-held eastern district of Akobo. From the air it doesn't look like a place on the brink of famine. The town sits by the beautiful Akobo River, a tributary of the White Nile, which snakes through green woodlands and marks the porous border between South Sudan and Ethiopia. But once you're on the ground the needs are palpable: here about one in three children aged under five are malnourished.

Akobo district is governed by a charismatic commissioner named Koang Rambang Chol. Standing about 210 centimetres, he is an imposing figure in his grey safari suit. Constantly flanked by two Kalashnikov-wielding bodyguards, one wearing thongs, Chol is a supporter of rebel leader Riek Machar and accuses the government of systematically killing people from his tribe. "We Nuer refer to it as genocide," he says. "I am a district commissioner; what reason do I have to rebel against a government I have served? I have been forced to rebel simply because of my ethnic background."

But officials in Juba insist there was no justification for the rebellion. "If former vice-president Machar wanted to be president, he could have gone to the people of South Sudan and sought their mandate," says Deputy Foreign Minister Peter Bashir Gbandi. "Our people don't deserve to be suffering again after such a long journey to independence ... the rebels have really committed massacres." A truce brokered in late August gave the warring sides six weeks to form a power-sharing government, although several earlier peace deals failed.

Chol tells me Akobo is calm and secure. But it feels like a town under siege. Rebel soldiers armed with Kalashnikovs and rocket launchers patrol the streets and there's a strict 9pm curfew. The mobile telephone system has been shut down, forcing aid workers to rely on satellite phones to communicate.

Chol says the government in Juba is refusing to send essentials like food, medicines and fuel to rebel-held areas. River trade with neighbouring Ethiopia has become a life-line for Akobo; if it were not for the Ethiopian traders who own many stores in the town's ramshackle market, the district's hunger crisis would be worse. Even so, the survival of tens of thousands of people in the region depends on what Chol calls its "humanitarian partners", especially the UN.

At a feeding centre at Denjok, a village about an hour by boat from Akobo, I watch as local aid workers distribute nutritious peanut paste to about 100 malnourished children. But supplies run out and some seriously under-weight children go home untreated. Several mothers tell me how they are being forced to forage for leaves and berries in the forest to feed their families.

In a nearby two-bed clinic made from mud, 13-year-old Ruot Deng Rambang is being treated for malaria. "He had it last year as well," says his father, Deng. "This time it's much more severe." The boy is in luck - the clinic still has some medicines to treat him.

One afternoon, local attention turns skyward as a giant World Food Program cargo plane, dispatched from Ethiopia, circles overhead. The Russian-made Ilyushin swoops over Akobo, three times dropping more than 30 tonnes of seeds that will help needy local farmers start planting crops again. But for many of Akobo's children, the next harvest is likely to come far too late.

In June, South Sudan was ranked the world's most fragile state by the US-based research institute Fund for Peace. "Decades of warfare and a complete lack of infrastructure left behind a state that was one in name only," wrote the fund's Patricia Taft. "It had virtually none of the capacities or functions of a nation other than a name and a flag."

It would be a tragedy if the diaspora population that returned after independence lost hope and fled the country again. But war and mass hunger have not yet broken the South Sudanese spirit, and I find the dream of a peaceful, prosperous nation is still very much alive.

The mood among the Australians on Juba's rooftop restaurant remains upbeat. "I am very optimistic about this country," says Akoc Manhiem. "Our people are very energetic and they do listen. That gives me hope that we can help move the people of South Sudan out of poverty and help develop a better system."