Part of our eight-month "Future of Food" series—exploring how to feed 9 billion without overwhelming the planet.

South Sudan, the world's youngest country, is on the verge of the world's worst famine.

The UN estimates that a third of the country of 11 million are facing starvation unless farmers can plant a critical round of crops before the annual rains hit in May.

Experts believe as many as 50,000 children could die. It would be the most devastating famine anywhere in 30 years.

Since December, when South Sudan's leadership splintered over suspicions about a coup plot, violence has spread across the country, disrupting the planting season, forcing hundreds of thousands of people to flee, and leaving more than 10,000 people dead.

"We're grappling with a whole host of issues now," says Toby Lanzer, the UN Assistant Secretary General and the senior UN official leading relief efforts in South Sudan. (Read "A Five-Step Plan to Feed the World" in National Geographic magazine.)

"The scale, depth, and ferocity of what has happened has engulfed this country as a tsunami would have done if we had a coast," says Lanzer.

Whether or not there's a famine, he says, could depend on what does or does not happen by the end of May: "This is crunch time."

A New Beginning

Just a few years ago, South Sudan's prospects were looking better than they had in decades. After half a century of strife—and very often outright civil war—with northern Sudan, the Republic of South Sudan became the world's 193rd country on July 9, 2011.

But when newly elected president Salva Kiir fired his vice president and one-time ally Riek Machar in July, accusing him of plotting a coup, it unleashed a wave of bloodletting in December.

The Sudan People's Liberation Army fractured, as forces loyal to Machar fled with him and at least ten other high-ranking officers to the countryside, where they mounted an insurgency.

The conflict quickly took on ethnic overtones. Thousands of Nuer tribesmen bent on vengeance for reprisals against them after Machar's ouster joined the rebel forces as proxy warriors in the fight against Kiir's ethnic group, the Dinka.

In the past five months, more than a million people have been displaced from their homes, including some 270,000 who have fled to neighboring countries.

View Images A boy carries chickens off a boat in Minkamen, a village in South Sudan where many displaced people now live, on January 11, 2014. PHOTOGRAPH BY PHIL MOORE

From Bloodshed to Brink of Famine

In a nation that was already struggling with health and nutrition problems, the violence has taken a huge toll on basic sustenance.

Looters and soldiers have ransacked thousands of pounds of food stores. International aid convoys that set out to restock them have been repeatedly stopped and attacked.

In the city of Acobo, some 2,000 armed youths overran a UN compound in December, killing two peacekeepers and reducing the base to rubble.

One problem is that the three states that produce most of the food for the rest of South Sudan—Jonglei, Upper Nile, and Unity—are also the ones where fighting has been heaviest.

In Upper Nile State, the country's breadbasket and the source of most of its sorghum—a drought-resistant grass grown across much of Africa—internally displaced refugees have flocked to the banks of the Nile River to escape the fighting.

There, they have been able to sustain themselves by fishing, hunting, and retrieving edible bulbs from water lilies that grow in the marshes. But when the river floods next month, they will face further displacement—and disease.

"Flooding will hugely increase the chances of epidemic waterborne diseases, including cholera," says Doune Porter, chief spokesperson for UNICEF in Juba. "The fighting is preventing farmers from planting crops, and time is really running out on them now."

View Images A woman and her children wait for medical care in a clinic in Minkamen on January 10, 2014. PHOTOGRAPH BY PHIL MOORE

The F-Word

For now, aid officials have stopped just short of declaring a technical famine.

In part that's because there are several different types of famine. The declaration can be based on measures of food supply, consumption, or mortality.

A "scrimshaw" famine, for instance, results from a sudden and drastic decline in food consumption, while a "Blix" famine is the more traditional "widespread food shortage" associated with the term. There are also gradations of a famine's severity, with levels increasing depending on the number of people affected.

Aid officials with the United Nations in Juba are referring to the crisis as "the F-word."

The UN's Lanzer says that unless international donors—mostly Western countries like the United States—can pony up some $230 million in the next two months, the current "extreme risk of food insecurity," could quickly morph into a full-blown famine.

Thousands of farmers have fled their fields to escape violence. Many of those who have stayed don't feel safe enough to plant a round of crops for fear the fighting could intrude at any time.

"If there isn't a planting season, there won't be a harvest," says Lanzer. "You have three to four million people in South Sudan on the brink, [so] the international community would have to mobilize very quickly."

Even before the current crisis, South Sudan had the world's highest rate of maternal deaths during childbirth, as well as exceptionally high rates of malnutrition. The conflict has made those and other problems more acute.

Thousands of children have been swept into the fighting, some as child soldiers, others as victims.

"Children have been killed and maimed and orphaned in the fighting and have witnessed terrible atrocities," says Porter, who recently returned from a trip where he saw dozens of families be reunited with their children after months of separation caused by the conflict. "It was total chaos."

The conflict is also forcing aid groups to improvise. South Sudan, roughly the size of France and with a population of around ten million, has only 200 miles of paved roads. The rest of the country is bisected by rust-colored dirt tracks, and most of these will become impassible once the rains begin, if they aren't already.

The World Food Program has already begun scheduling food drops by air, and UNICEF is considering creating packages of nonfood essential items that could help people already struggling with food shortages. These include plastic buckets for hauling water, mosquito nets, and water purification tablets.

In addition, the World Health Organization and the UN's Food and Agriculture Organization have started sending small teams of between six and eight people by air to the most vulnerable in the hardest-to-reach areas.

They have completed four missions, with three more scheduled for the next week. "There's a lot of experimentation that we need to do," says Porter. "What do people need to survive? How do we package it? We're trying to find new ways of reaching people."

View Images Women and children collect water near Minkamen on January 10, 2014. PHOTOGRAPH BY PHIL MOORE

Waiting for Signs of Fallout

If famine does strike South Sudan, the first signs of fallout won't likely appear before December or January, when the harvest comes back empty. Well before then, however, in June, the UN plans to assess how many counties planted successfully.

There are some small signs of hope.

In Western Equatoria State, there has been less fighting and farmers have begun to plant. While that's good news for locals, the rest of the country won't see the benefits. "That one state can't ship to any others," laments Lanzer. "The markets aren't sophisticated in that way."

In the meantime, both government and rebel forces have responded to international aid efforts to stave off the looming food crisis with more violence and finger-pointing.

"Our personnel have been beaten up; we've had people threatened at gunpoint in various contexts," says Joseph Contreras, spokesperson for the UNMISS peacekeeping mission. Some of that violence has subsided in the past few weeks, but the threat of mass starvation hasn't brought the two sides closer to a resolution.

Contreras said staff members from his group are monitoring the talks and trying to push the parties toward finding common ground.