Not all new countries are really new. Some are born almost fully formed; others have to start from nothing.
That difference is crucial to a new nation's chances of success.
More than half the youngest nations in the world were born or reborn after the collapse of communism in Europe and had existed as independent states as far back as the Middle Ages. Most regained independence with established institutions - courts, banks, police forces, schools - and skilled people to run them.
After an initial decade or so of wrenching economic change, places such as Croatia, Estonia and Slovenia began to boom, boosted by the promise of membership of the European Union. Former communist states such as the Czech Republic have come through the global financial crisis in better shape than richer neighbors.
At the other end of the spectrum are far poorer young nations such as South Sudan, Eritrea and East Timor, all born following armed struggle and boasting far fewer institutions and far fewer of the type of skilled bureaucrats countries need if they are to prosper.
South Sudan, whose first year Reuters has chronicled in a series of special reports, is the most extreme example of that. When it won a measure of autonomy from Sudan in 2005, its roster of organized, national institutions began and ended with its army.
The desire to secede was understandable. Most Southern Sudanese had - and have - profound ethnic and religious differences with their former rulers in Khartoum, who alternately neglected or fought the south.
But when it gained full independence last year, just one in four South Sudanese adults could read or write; only two percent of children are enrolled in secondary education. It still has only 300 km (186 miles) of paved roads. Over a quarter of the population will require food assistance this year.
If South Sudan's more developed neighbors - places such as Ethiopia and Chad - are any measure, the newest nation on the planet will have to rely on the United Nations and aid groups for years to come, even if it develops quickly and smoothly.
"In the case of South Sudan, you don't reconstruct, you don't rebuild, you start from scratch," Hilde Johnson, the U.N. Secretary General's Special representative for South Sudan, told Reuters just before the first anniversary of independence in July.
A Reuters examination of more than a dozen key indicators in the 31 nations founded or reconstituted since 1990 shows just how steep a climb South Sudan faces (see chart for six key indicators).
Almost all the most successful new countries had a welter of winning traits from the start: stable and often generous neighbors, strong institutions, homogenous and well educated populations, and relatively low corruption.
The best performing - places such as the Czech Republic, Slovakia, Lithuania, and Estonia, as well as the single most successful, a reunited Germany - have been those with the longest prior experience of nationhood and centralized government. They are also, strikingly, countries with more limited natural resources of their own, and economies built on commerce and trade.
On measures including life expectancy, perceptions of corruption, education, press freedom and the rule of law, the former communist nations of Eastern Europe have generally improved more than new countries elsewhere.
In contrast, resource-rich states such as Russia, Turkmenistan, Uzbekistan and Kazakhstan have performed well on aggregate figures such as GDP per capita, but rank close to the bottom when it comes to effectiveness of government, rule of law and transparency. This is unsurprising. Economists have long known that the combination of weak institutions and easy cash can be particularly destructive.
One of the worst performing new countries by many measures is Yemen, a fusion of two struggling states with a dysfunctional economy and little tradition of effective government. While the country has begun to tap its reserves of natural gas, corruption and one of the fastest growing populations in the world are likely to keep its people poor.
It's not all bad news. Many of the very poorest young states have seen improvements in income and health over the past couple of decades. Even when international aid has not been able to keep the country stable, it has often saved lives.
Two of the most troubled, Yemen and Eritrea, have experienced significant improvements in life expectancy. Infant mortality has fallen in all of the newest 31 nations, and children are spending more time in school. Even in Somalia, generally regarded as the world's most troubled state, international handouts have kept child mortality from rising sharply.
And there are exceptions to these trends.
Development experts hope that East Timor may join the short list of developing nations to escape the resource curse - in which natural resources hurt growth rather than boost it.
East Timor, which split away from Indonesia in 2002, has been helped by billions of dollars worth of oil and gas. With the aid of advisers from model nations such as Norway it has built up more than $11 billion in a fund created to ensure good management of its oil and gas money and make sure that its 1.1 million people have something to live on when the resources run out.
The tiny Indian Ocean state also has powerful friends - in particular Australia, which has provided troops several times to stabilize the country during periods of unrest.
But even good friends don't guarantee success. For all its support from the West, and despite rapid economic growth, the former Yugoslav Republic of Kosovo has struggled with corruption and organized crime. It doesn't help that the country still exists in a state of legal limbo, un-recognized by Moscow or Beijing and heavily dependent on the UN, EU and NATO for aid and protection.
The kind of massive aid and institution-building efforts deployed in South Sudan over the past few years show particularly mixed results, even in countries that are not starting from scratch. A multibillion-dollar aid and military mission to Somalia in the early 1990s did little to stop it falling deeper into chaos (though in the past few months it has finally shown signs of progress, in part thanks to an African peacekeeping mission).
Peacekeepers, development experts and billions of dollars of aid in the Democratic Republic of Congo and Haiti continue to struggle to keep the peace and even basic services running.
Writing in Britain's Guardian newspaper last week, Richard Dowden, head of the London-based Royal African Society, argued that Congo has been hurt most by its politics. "Aid has probably made things worse by offering development which may never be delivered," he wrote. "There is no state capable of delivering it. If ever there was a case for a country to be under a UN mandate, it is Congo. The United Nations' current half-baked, ill-thought-out mandate was cruelly exposed last week as UN troops stood back to allow rebels to take the city of Goma in eastern Congo."
The United States and other powers supported the birth of South Sudan not because they thought the country had brilliant prospects but because independence looked better than the alternative: the continuation of a decades-long civil war that had claimed some 2 million lives. The southern rebels and their Western backers - including evangelical churches and campaigners in Washington DC - had made a convincing argument that South Sudan deserved to be free.
But freedom brings fresh challenges.
"The international community can't build countries," says John Temin, a veteran former humanitarian worker and now head of the Sudan project at the United States Institute for Peace, a U.S. government-funded think tank. "Countries have to build themselves. We can only help. We are getting very good at stopping people from dying, but we're not good at building institutions."
South Sudan's deputy health minister, Dr. Yatta Lori Lugor, believes the problem often lies with those seeking to help as much as those receiving aid. "In general (non-governmental organizations) help but some of them come just for themselves," he said. "This is very frustrating."
Can South Sudan, the world's 193rd country by the United Nations' count, prosper? In its first 16 months it has come close to war with its old masters and rivals in Khartoum, seen several ethnic massacres, the biggest of which killed more than 800 people, and had to survive without 98 percent of its income Amid an oil-industry shutdown.
Such problems are to be expected, according to John Christofides, a former head of the United Nations Department of Peace Keeping Operations' South Sudan team and now in charge of all other peacekeeping operations in Africa. When it comes to nation-building, "you often find the operation will be in the country much longer than you expected."
For Garang Kuach, the County Commissioner for Aweil West, that misses the point.
"This is our land," he said, standing in Freedom Square, a patch of dusty earth in the town of Gok Machar, half an hour's drive from the border with Sudan. "You cannot say it is yours. (Independence) is better for us. It gives us freedom."
(With reporting by Amna Bagadi, Costas Pitas, Clare Hutchison, Sophie Walker and Sara Ledwith in London, and Hereward Holland in Gok Machar, South Sudan; Edited by Simon Robinson)