South Sudan gained independence in 2011. That makes it the world's youngest nation. But now, this new state is in chaos. A civil war has broken out, and the U.N. Commission on Human Rights in South Sudan recently warned that "the stage is being set for a repeat of what happened in Rwanda."

Indeed, ths extremely poor country without strong institutions is in the grips of ethnic warfare. "There is already a steady process of ethnic cleansing underway in several areas of South Sudan using starvation, gang rape, and the burning of villages," said Yasmin Sooka, the U.N. envoy. "Everywhere we went across this country we heard villagers saying they are ready to shed blood to get their land back. Many told us it's already reached a point of no return."

As many as 300,000 people are estimated to have died, and three million of the country's 12 million people have been displaced.

It wasn't supposed to be this way. South Sudan was midwifed by the international community to prevent a genocide. At the time, Sudan's central government, led by the thuggish dictator Omar Al-Bashir, who represented the mostly-Arab and mostly-Muslim North, was waging a campaign of genocide against the mostly-Christian and Animist and mostly-black inhabitants of the South. Oil had recently been found there, and Al-Bashir wanted it. But the Bush and Obama administrations, the U.N., the EU, NGOs, and a parade of Hollywood celebrities fought for the cause of South Sudanese independence.

What has happened in the years since is a depressingly common tale: Ethnic tensions have blown up amidst weak institutions and weak national identity. The country's most populous tribes, the Dinka and the Nuer, were supposed to share power in the new government. South Sudan's first president, the cowboy hat-wearing Salva Kiir, a Dinka, even appointed Riek Machar, a Nuer, as vice president.

But the two men have fallen out, and the two tribes did not manage to build a government together. Given South Sudan's oil, many former freedom fighters expected a lot of money to come their way to rebuild the country and build up its institutions, and well, give fighters something to do that wasn't fighting. This hasn't happened. Since Kiir and Machar have fallen out, both sides have started taking up arms and engaging in a destructive vendetta. And now, the conflict has also become about who controls what land, in a country that has a long tradition of pastoralism and very little history of statecraft, which means that property rights are more theoretical than they are real.

At bottom, South Sudan is in such chaos because it doesn't have, and never had, the strong institutions of state necessary to ensure economic development and to give people a stake in the country as a whole, as opposed to their ethnic tribe. Peacekeepers to stop the shooting would be a good start, but they won't get at the root causes of the conflict. What South Sudan needs is nation building; an international group with legitimacy, whether it is the U.N., the African Union, or an ad-hoc body, needs to bolster the country's infrastructure and institutions.

What would this look like on the ground? Well, for example, fighters should be integrated into a "proper" army and police force, which would aggregate and mix members of different ethnic tribes. This force would be well paid and well trained, so that armed forces aren't beholden to a particular ethnicity or grandee. Schools and health centers should be built and staffed. Community-driven agricultural projects should be set up. These initiatives wouldn't require much money, relative to the countless billions the international community spends on aid to Africa, but they would require dedication and expertise over the long term, not just a quick-fix approach. And that is what is missing most.