Things are spiraling downward in South Sudan, one of four nations where, according to the U.N., the greatest humanitarian crisis since 1945 is unfolding.

And in the case of South Sudan, it's not drought or climate change that's causing the catastrophe. It's civil war.

Last month the U.N. declared a famine in two parts of the country and warned that nearly half the population is in urgent need of food assistance.

Soon after this declaration, the American relief agency Samaritan's Purse was forced to pull most of its staff out of one of the famine-stricken zones because of fighting in the area. A skeleton crew of 7 local staff members remained behind. Then on Sunday, armed gunmen abducted those workers.

A spokesman for the South Sudanese military said the aid workers were being held for ransom by rebel fighters demanding food aid in exchange for their release.

On Tuesday, Samaritan's Purse confirmed that their employees had been let go.

"At the very moment that we are talking they are in a helicopter on their way to Juba. They've been released," says Ken Isaacs, vice president of programs for Samaritan's Purse, who spoke to NPR by phone earlier today from the aid agency's headquarters in North Carolina.

"I think they're OK. I don't know if they were manhandled. We are under the assumption that they're safe, OK and they're headed out." Negotiations involving local military leaders on both sides of the conflict, he says, brought about their release. He adds that no ransom was paid.

The abduction, however, has forced the aid group to halt operations in the epicenter of one of the worst famines in the world.

"This incident clearly illustrates the complexities and dangers of working in South Sudan," Isaacs says. At the same time that people are starving, fighting has turned parts of the country into no-go zones for relief agencies.

This same pattern is playing out in three other countries in the world right now, prompting the U.N. to declare that it's facing the worst humanitarian crisis since World War II.

Violence in Yemen, according to the U.N., has left 18 million people — nearly two-thirds of the country — in need of humanitarian aid. Drought combined with chaos and extremist militants in Somalia are leaving millions hungry there. And in West Africa, Boko Haram fighters have terrorized people across large swaths of Northern Nigeria, driven farmers from their land and left a massive food shortage in their wake.

Back in South Sudan, another area where famine has been declared is Leer County, just south of where the Samaritan's Purse team was working.

Nellie Kingston, emergency coordinator for Concern Worldwide in South Sudan, visited Leer last week. Reached by phone in the capital Juba, Kingston says Leer is a wasteland.

"I saw no planting in Leer County. Villages are deserted. People are hiding in swamps to avoid the fighting," Kingston says. Most of the fit, able-bodied residents have fled to camps set up by the United Nations, she says. Those left behind have almost nothing to eat.

"The people I met are living on what they can forage in the swamps where they live. Luckily those people have access to fish [from the swampy water], which adds some protein to their diet."

Kingston says this is a manmade food crisis. Fighters from both the government and the rebel side in the war have been accused of robbing, raping and killing civilians. Gunmen have torched crops and chased farmers from their fields.

Logistically, she says, it's very hard for aid agencies to deliver food rations to people hiding in remote swamps. And when the rains hit later this spring, she says, most of the dirt roads will turn to rivers of mud, making the delivery of aid across much of Leer County nearly impossible. "In the next rainy season, those people are locked into where they are," she says.

The World Food Programme has been trying to reach some of them by dropping bags of grain from airplanes into some parts of the country. Last year the WFP distributed a record 265,000 metric tons of food supplies by air and truck across South Sudan, the most since South Sudan gained independence in 2011.

Ken Isaacs of Samaritan's Purse says that just when it looked as if things couldn't get any worse in South Sudan, the country has become even more chaotic.

"If something isn't done to bring a stable government to the area soon," he says, "we are going to see much more loss of life and a lot more bloodshed."

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