JUDY WOODRUFF: But first: South Sudan, the world's youngest country, founded in 2011, is in freefall. Three of its six years in existence have been spent fighting a civil war that has left tens of thousands dead.

Now the ravages of that war have led to a manmade famine. Last week, the United Nations reported that 7.5 million people there are in need of assistance.

From South Sudan, John Ray of Independent Television News brings us this report.

And a warning: Viewers may find some of the images upsetting.

JOHN RAY: Of South Sudan's many torments, hunger has become the greatest terror of all. It is a horror written in the flesh and bones of this little boy. It has drawn the strength from his limbs and the life from his eyes. His name is Khamis, 2 years old, but weaker than a newborn baby.

His mother has lost one child to sickness, lost family to war, and now starvation threatens her son.

LOMO LATABO, Mother (through interpreter): There is no food. Anything we can find, we will try to eat. We find grass, we will eat it. That's just the way it is for us now.

JOHN RAY: The red warning signs are everywhere. At this screening center out in the countryside, we're told four out of every 10 children are severely acutely malnourished. In language any parent would understand, they risk starving to death.

So, with every exhausted step, South Sudan moves from the brink of genocide into the arms of famine. For many days and many miles, they have trekked across a sand-blown wasteland in search of something to eat and somewhere safe to stay.

Exhausted, famished, almost finished, and all they have gained is the shade of a tree. Everyone is hungry, the old woman tells me, but better here than at home.

WOMAN (through interpreter): The soldiers came, and so many people were killed, even the women and old people. My children were shot in front of me. The houses were burnt, so we ran to the bush.

JOHN RAY: There is food, but nothing like enough. In the district center of Ganyiel, a U.N. plane has just delivered its once-a-month aid drop. And in the baking heat, they collect their rations, but thousands have arrived too late.

We found this woman picking through the dirt for a few grains split from the sacks of cereal. In the long grass all around, there are many like her. This is all she has for the next month.

"It shames and pains me," she says, "but how else can I live?"

The answer, for many, is to risk the malaria-infested marshes that line the River Nile. We watched William Gaul and his family of eight children arrive after a 19-day journey from famine through fighting. All they have eaten on the way are water lilies.

WILLIAM GAUL, South Sudan (through interpreter): I have never seen so many people die of hunger. Only God can help us now. Without God, I am afraid none of us will survive.

JOHN RAY: This is Dalia, 6 years old, perilously thin. Her fight for life is one tiny front line in a much wider struggle, 100,000 people on the verge of starvation. Dalia is precisely the same age as her country, uncertain fates intertwined.

But, like so many children, Khamis knows only fear and hunger, first the war, then the famine, now the reckoning.