When war came to 15-year-old Rebecca Riak Chol’s small town in rural South Sudan in early April, she and 27 other villagers fled into nearby marshlands to hide. They spent two grueling weeks slowly making their way to the relative safety of a region controlled by rebels from her same tribe. They were constantly hungry, constantly thirsty, and constantly in danger of being killed by the troops trying to hunt them down. Chol’s sister died along the way, but it wasn’t because she was found and shot. Instead, she — like growing numbers of South Sudanese — died from starvation.

“We didn’t have anything to dig with to bury her, so we just put grass on the body and left it there,” Chol told me during a conversation in the schoolyard of her new home in the small town of Thoahnom Payam. Two school buildings with mud walls and tin roofs flanked the dry dirt yard. In the center was an unused volleyball net.

One of Chol’s classmates, 16-year-old Marco Nuer, arrived here in February from a different violence-ravaged part of the country. Like Chol, he paid an enormous price: His father, brother, and sister starved to death along the way. He and his mother were the only ones to survive.

The two stories are tragically common in South Sudan, which is facing mass hunger on a scale unimaginable in almost every other part of the world. In February, the United Nations estimated that 100,000 South Sudanese were starving, and that 5 million more — 42 percent of the country’s population — have such limited access to proper food that they don’t know where their next meal is coming from. More recent figures are not available yet, but aid agencies fear the situation could be much worse now.

There are two things you need to understand about the famine decimating South Sudan, the world’s newest country and one that came into existence largely because of enormous assistance from the US.

First, South Sudan isn’t the only country in the region facing mass starvation. A potentially historic famine is also threatening Nigeria, Somalia, and Yemen. Far from Western eyes and far from the headlines, an estimated 20 million people in those four countries are at risk of dying due to a lack of food.