YAMBIO, South Sudan — Simon Burete was weeding his peanut field a few weeks ago when he saw smoke coming from his house. He ran as fast as he could.

He and his wife, Angelina, had enjoyed years of peace, he farming the fields, she selling the produce in the market. They were poor but welded to each other. Just that morning, they had talked about walking into town to buy their first mobile phones.

But as Mr. Burete made it back to the house, out of breath, red dirt still stuck to his knees, he couldn’t believe his eyes. His wife was lying on the floor, burned to death in a rampage by government forces.

“I used to call her akara-ngba,” he said, which means in the Zande language “the last word on beauty.”

He could barely choke out the words.

South Sudan’s war and its full ugliness are engulfing new, previously peaceful areas of the nation, spelling horror for the victims and signifying something deeper: This country is cracking apart.

Yambio, a midsize town of wide dirt roads and lofty kapok trees that seem to breathe tranquillity, used to be part of what was called a green state. This place was considered safe. It was not a red zone.

But now charred buildings and crushed huts line the roads leaving town. Bountiful fields — here in a part of the country known as South Sudan’s breadbasket — lie untended during a desperate national food crisis. The names of dead loved ones circulate through hastily built displaced-persons camps all around Yambio, just as they do in cities and towns hundreds of miles away.

South Sudan’s conflict started as a power struggle between the country’s political leaders before slipping into a broader feud between the two biggest ethnic groups, the Nuer and the Dinka.

But as it enters its fourth year, this war, Africa’s worst, is rapidly sucking in many of the nation’s other ethnic groups, including the Azande, the Shilluk, the Moru, the Kakwa and the Kuku. The widening conflict is imperiling nearly every pillar that this young country’s future rested on: oil production, agriculture, education, transport and most especially unity, which seemed so proudly on display six years ago when South Sudan was born in a halo of jubilation that now seems Pollyannish.

Tens of thousands of civilians have been killed, and every major cease-fire that has been painstakingly negotiated by African and Western officials has been violated.

Dangerous fissures are opening up within the South Sudanese military, and the burst of bloodshed here in the Equatoria region is both cause and effect. An Equatorian general and a colonel recently quit, criticizing the government on their way out. One said the justice system was “too deformed to be reformed.” The other accused the government of orchestrating a “tribally engineered war.”

On top of all this now comes another calamity: famine.

Last month, the United Nations declared that parts of South Sudan, which receives billions of dollars of Western aid, were suffering a famine.

A formal famine declaration is rare — in the past 25 years, only a handful have been made worldwide. They are a cry for help (and for donors to give more money) and an admission that aid efforts have catastrophically failed. Blaming the South Sudanese government and rebels for intentionally blocking lifesaving supplies, United Nation officials said more than one million people could die.

The hunger-stricken areas include some of the same ones afflicted during South Sudan’s last famine in 1993, immortalized by a Pulitzer Prize-winning picture of a vulture squatting behind a starving toddler too exhausted to crawl.

A Repeat of Atrocities

The United States helped birth this nation, building ministries, training soldiers, pumping in more than $11 billion since 2005. Americans, especially powerful Christian groups, cheered on the South Sudanese rebels during their decades-long liberation battle to split off from the Arab-dominated government of Sudan, which southerners simply called “The North.”

But South Sudan is going down the North’s same bloody road.

By all accounts, South Sudanese soldiers have become brutal doppelgängers of the widely vilified northern Sudanese forces that they had rebelled against, waging war ruthlessly against their own people.

Analysts say South Sudan has become shockingly similar to Darfur, the vast, western region of Sudan that plunged into conflict in the mid-2000s and became a global byword for atrocities against civilians.

What happened there is happening here: government-backed militias, and sometimes uniformed soldiers, sweeping into towns, burning down huts, massacring civilians, gang-raping women and driving millions from their homes, leaving many to crowd into disease-ridden camps protected by United Nations peacekeepers.

Human rights groups say the evidence of war crimes grows by the day. And just as in Darfur, United Nations officials in South Sudan are worried about genocide.

The South Sudanese government says it is putting down a rebellion — the same rationale used in Darfur. And it is true that armed groups rose up in 2013, led by ambitious Nuer politicians challenging Dinka hegemony just two years after South Sudan won its independence from Sudan.

But the broader narrative of the two countries is beginning to blur. A commonly uttered line on Sudan is that it has been at war with itself since independence. Most analysts and even some South Sudanese government officials fear that could be South Sudan’s destiny as well.

“We are doing exactly what the North was doing — that is the irony,” said John Gai Yoh, an adviser to South Sudan’s president, Salva Kiir.

“I feel my life is meaningless,” Mr. Yoh said, sitting in a large office in Juba, the capital. “Why is it that we had to fight all these years and end up here?”

He said he stayed on as a presidential adviser because if people like him left, “the whole system disintegrates.”

Dinka Domination

South Sudanese officials admit that their government, led by Mr. Kiir, has been a huge disappointment.

Take the economy. When South Sudan gained independence, it was churning out 300,000 barrels of crude oil per day, generating billions of dollars that were supposed to be spent on schools, roads, playgrounds, health clinics, water treatment facilities, police stations, all the gear of a functioning state.

But look around most of South Sudan and you won’t see any of that. The reason? The oil revenue was stolen. Top officials have been accused of amassing fortunes, and they and their families were often spotted in Nairobi, the capital of Kenya next door, driving the snazziest cars — $100,000 Land Rovers and gleaming Humvees that hogged up the road.

Back in South Sudan, teachers are paid less than $3 a month, and many said they hadn’t seen even that. Even ambassadors often don’t get paid.

A few years ago, the government struck a questionable revenue-sharing plan with Sudan. Instead of insulating themselves from oil shocks, as outside consultants urged, the South Sudanese cut a deal to make as much money as possible when oil prices were high.

But once oil prices collapsed, the costs of production were nearly as much as the market price, leading to almost no government revenue or foreign exchange and causing enormous inflation, which in turn has fueled the famine. For many South Sudanese, food prices have spiraled out of reach. And now that the war has disabled many pumps, oil production is a trickle.

One of the few shards of hope, analysts say, is that Riek Machar, the former vice president and powerful Nuer politician who led the rebellion against the president, has been sidelined, relegated to exile in South Africa. Mr. Machar has been widely blamed for stoking ethnic violence and was considered a destabilizing force in the 1990s during the liberation battles, and few of South Sudan’s neighbors, which have been trying to broker a peace, want him to return.

But the issue of Dinka domination remains. The president, Mr. Kiir, is a Dinka, as are the chief of staff of the army and many top military and security officers.

Government officials admitted that some of their soldiers had committed abuses, but the government denies that it is trying to stir up an ethnically driven war.

In Yambio, most people are from the Azande ethnic group, and many say they have been brutalized by the Dinka. They also say some of their youths have joined the fight against the government.

They call the rebels “the boys in the bush.”

It’s often hard to tell which came first, the oppression or the rebellion.

In the past few months, small bands of Zande rebels have attacked government convoys and the houses of government officials. In response, the government has gone on a tear.

United Nations officials said that in December, government soldiers, commanded by Dinka officers, had burned down a string of villages outside Yambio and massacred scores of civilians. In Yei, another town in the Equatoria region, United Nations officials said that government soldiers chopped up babies and threw the body parts in a river.

The villages around Yambio have turned into ghost towns, empty huts staring lonesomely out at the wide dirt roads. Fields of peanuts, cassava, beans and corn have been abandoned. Some of the skinny papaya trees are so full of fruit at the top that they look like they’re about to tip over. Nobody’s around to pick them.

‘Left Me for Dead’

Yambio was considered one of the best educated, peaceful and agriculturally productive parts of the country, but farmers have fled to camps for the internally displaced. The people here are now totally dependent on donations from aid groups, adding to the strain in dealing with the famine.

Few want to return home, fearing their own government.

“Six Dinka commandos raped me,” said one woman in Yambio, who asked that her name not be used for fear of reprisals.

Not far away, David Angelo, 22, looked over his shoulders before slowly taking off his shirt. Standing in the sunlight, in front of a tiny hut in a displaced persons camp, he said he was not a rebel but had been captured by Dinka soldiers bent on revenge.

His back, his neck and his shoulders bore fresh machete scars. “The government soldiers left me for dead,” he said.

Some analysts, both African and Western, feel the situation is so hopeless that they have proposed a radical solution: an international takeover. The argument says that South Sudan’s government is not an effective or legitimate state, and that it should be nudged aside to let the United Nations and the African Union run a transitional administration for 10 to 15 years. South Sudanese officials say they would violently resist this.

“We went wrong,” said Taban Deng Gai, the first vice president. But, he added, “South Sudan is not a banana state.”

Many South Sudanese are now asking questions they thought they would never ask: Should they have voted for independence? Would their lives be better if South Sudan were still part of Sudan?

These questions are academic for Mr. Burete, whose eyes shine with tears when he remembers his wife.

He recalled how, at the end of each day, she would show him the money made from selling vegetables. If it was a good day, they would treat themselves to something special.

“She loved to eat meat,” he kept saying. “She loved to eat meat.”