JUBA, South Sudan — The hunger season came early this year.

By February, once seen as a time of plenty, Nyabolli Chok had run out of food for her three children in their village here in South Sudan. She knew they had to leave.

“We were eating leaves off of trees,” she said, describing how she boiled them into a watery soup.

“Ron reath,” she said — her words for the hunger season. South Sudan’s dozens of ethnic groups use different names for the months when food becomes scarce until the next harvest. But the fears are the same: malnutrition, disease, even death.

And this year is expected to be the worst yet.

More than four years of civil war — most of this young country’s existence — have chased millions from their homes, leaving countless farms abandoned. The economy has been obliterated. Fighting has overcome some of the nation’s most productive land. Food prices are ruinously high.

Even during harvest time in January, when food was most abundant, more than five million people — almost half the population — did not have enough to eat. Now, as food runs out over the next few months, international officials expect that number to grow considerably, with millions potentially facing acute malnutrition.

This year’s harvest was the smallest on record since South Sudan gained independence from Sudan in 2011, with the country producing only a fraction of its needs, according to the World Food Program.

On top of that, peace talks have stalled and cease-fires have largely been ignored, which means the fighting has cut off some areas from emergency help. Aid workers have even been targeted by government and rebel fighters alike, making food distribution increasingly difficult.

Even here in the capital, which had been largely immune to the food crisis, many families are finding it impossible to pay the steep prices demanded in the city’s markets, their options vanishing as the currency crashes.

Families from across the country pile into a clinic for malnourished children, setting aside the political and ethnic divides that have torn this new nation to shreds. Some mothers come from areas backing the government. Others have husbands, brothers and sons who fight for the rebels.

Dozens of the women lie outside on the floor, their children wrapped in blankets. The signs of malnutrition are clear: Swollen bellies and emaciated limbs. Skin hanging in folds from tiny bones. Bodies covered in open sores, the painful result of edema breaking the skin.

Cecilia Kideen struggled to feed her 9-month-old daughter Sarah. Her breast milk is not enough, as she barely eats one meal a day.

“The mothers,” she said, “are really suffering.”

South Sudan, the world’s newest nation, was born from an enormous international push to end decades of conflict between the north and south of what was then Sudan.

But just two years later, the new country was at war.

In December 2013, a feud between forces loyal to President Salva Kiir and Vice President Riek Machar quickly descended into a conflict that has fractured the nation, killed tens of thousands of people and decimated what was already one of the world’s least developed nations.

“There are very few populations that are escaping the impacts of hunger,” said Elizabeth White, Oxfam’s South Sudan policy adviser. “But all roads lead back to conflict and insecurity.”

Talks between the government and opposition leaders have been postponed. But even if peace can be reached, the hunger crisis still looms.

The civil war in South Sudan has set off the largest refugee crises in Africa since the Rwandan genocide, the United Nations says. More than two million people have fled the country, crippling food production. Nearly two million others have abandoned their homes and remain scattered around the country, leaving behind ghost towns and untended fields.

At the nation’s southern border, dozens of refugees cross a narrow bridge into Uganda each day, bringing stories of hunger with them.

Mary Yar, 20, arrived with her 1-year-old son at a small reception center on the Ugandan side. At the site, the first assessment refugees go through is a malnutrition screening

“There is no food there,” Mrs. Yar said of her home village, pointing back toward the bridge to South Sudan.

During the height of the hunger season last year, South Sudanese refugees arrived by the thousands, said Geoffrey Chandiga, a child assessment officer.

He keeps a tally of new arrivals on a whiteboard, noting that officials are bracing for an uptick in refugees in the months ahead.

Two years ago, South Sudan’s war expanded into southern parts of the country that had long been seen as the country’s breadbasket. People flooded across the Ugandan border. Most have yet to return.

When United Nations peacekeepers visited the areas in early 2017, they saw entire villages burned to the ground.

Under a sharp midmorning sun in the capital, Elizabeth Kenyi and her husband, Johnson Ali, plucked vegetables from their garden along the White Nile, a tributary of the Nile.

For two decades, they have sold their okra, peppers and tomatoes in a nearby market. But even with a plentiful harvest this year, they are finding it harder than ever to feed their family of seven.

“The money that I got from the garden is useless,” Mr. Ali said.

While their produce commands a higher price than it did last year, prices for the staple grains they buy, like maize and sorghum, are climbing fast.

South Sudan’s currency is in free fall and hyperinflation has squeezed virtually everyone. Before the war, one American dollar was worth about five South Sudanese pounds. By March, a dollar was worth about 220 pounds.

The impact has been devastating. A 2017 World Food Program report determined that the relative price of a meal in South Sudan was among the highest in the world.

It found that people here typically needed to spend 155 percent of their daily income for a single plate of bean stew. To put it another way, a meal that would cost a New Yorker just $1.20 would cost someone in Juba the equivalent of $321.70.

With agriculture in tatters, emergency aid is keeping a growing share of the country alive.

By early 2018, half of South Sudan’s population relied on food aid, according to the United Nations, and the percentage will grow as the hunger season reaches its peak in the coming weeks.

But delivering that aid is another matter entirely. The rainy season hits during these lean months, too, turning many roads into rivers of impassable mud.

Beyond that, at least 100 humanitarian workers have been killed here since the start of the conflict, 30 in the last year alone, targeted by warring parties that think the efforts are helping their enemies.

Even within the protected camps set up around the country by the United Nations, there is not enough food to go around.

Mrs. Chok, the woman who boiled leaves for her children, had been at a protected area in Juba for a month. The camps sprang up in 2013 as ethnic minorities who feared violence from government forces and their supporters fled to the base of the United Nation’s Peacekeeping mission. Many stayed, and the camps have sprawled into makeshift cities ringed by barbed-wire fences.

The United Nations provides food to registered camp residents, but thousands inside have no official status, so they rely on their neighbors for food. The rations are simply not enough.

Aid workers say that so much of the country is on the move — with vast numbers of people fleeing places where violence erupts — that most new arrivals to Mrs. Chok’s camp have not been registered in more than a year. That means she and countless others receive nothing.

Staying inside the camps is dangerous enough. Attacks and sexual abuse by camp officers have been widely reported. Other accounts have emerged of women trading sex for food. But leaving the camp brings an entirely new set of risks.

Tafisa Nyattie, 30, who has lived in a camp here since 2013, has six children. Her food rations regularly run out, so she leaves the camp daily to gather firewood, hoping to earn enough money for milk and soap to wash her children’s clothes.

She walks up to three hours in each direction, braving threats from government forces before returning with a large bundle of wood on her head.

“They will rape you or beat you, and sometimes they kill you,” Mrs. Nyattie said, recounting the well-documented dangers women have faced in the conflict. “Some government soldiers tried to rape me.”

On another day, she said, she was beaten and her leg was badly injured. But when she saw how hungry her children were, she decided she had no choice but to head back out again.

“You just go, and you don’t know if you will come back to your children,” Mrs. Nyattie said.

The malnutrition clinic offers a chilling glimpse of what this hunger season may hold.

The hospital ward, frequently dark because of intermittent electricity, is treating nearly a dozen more children each day than it did this time last year. They come from around the country to be weighed, measured and given antibiotics and a milk formula before moving onto Plumpy’Nut, a peanut-based nutritional paste — if their bodies can handle it.

Many of the families here are not even victims of the horrors that have chased millions from their homes. Some have jobs, career plans and families to lean on — yet their children are still going hungry.

Selwa Anania, a restaurant worker from Juba, brought her 2-year-old son, Taban Zacharia, to the clinic. Her small salary does not go far in the market. Most days, it is only enough for a single meal of porridge.

Sylvia George, 27, fanned her 2-year-old son, Mandela Bisa, who lay half-conscious on a bed, hooked up to an intravenous drip. The child’s father is a student at Juba University, and the three live with Ms. George’s mother, whom they rely on for food. There is never enough.

For now, with the peak of the hunger season still weeks away, the clinic manages the steady flow of patients, said Josephin Ruben, the head nutritionist.

But, she noted anxiously, there “will not be enough when we get to June and July.”