The killing field on the edge of town is marked by skulls and bones littering the ground, attracting vultures and hyenas.

There is little clothing, for the soldiers stripped the men and boys they seized. Spines have been sliced in half and clavicles shattered, suggesting that victims were clubbed to death or hacked apart with machetes. Some of the skulls might even belong to five staff members of Doctors Without Borders who were murdered here.

Atrocities happen all around the world, of course. But these were crimes against humanity committed by “our side” — by the government of South Sudan that the United States helped to install.

It’s impossible to calculate the death toll, but it seems to me plausible that as many civilians are dying in the war here in South Sudan as in Syria. One reason it’s hard to estimate is that many civilian deaths here come not from bullets or barrel bombs, but from starvation and disease arriving as a direct result of war and ethnic cleansing.

This is the world’s newest country, midwifed by the United States in 2011 after a brutal war of secession from Sudan. Yet now the applause has faded, the United States has mostly moved on and South Sudan has tumbled into a mire of civil war.

Fighters mostly don’t confront each other, for that would be dangerous. So they kill, rape, rob and torture unarmed villagers. Meanwhile, an international appeal for humanitarian aid for South Sudan is only 3 percent funded.

I’ve been traveling through some of the areas most affected by fighting, in both government- and rebel-controlled areas, and they are in ruins that remind me of Darfur. Villages have been burned, hospitals pillaged, schools closed, boys castrated and women kidnapped and raped.

Roads are dangerous and often impassable, and there are no real government services — except executions.

Leer, a market town, was attacked by government troops in May and pillaged again by government-backed forces in October. The troops looted a hospital operated by Doctors Without Borders and the compound of the International Committee of the Red Cross, leaving part of Leer a ghost town.

What’s wrenching is both the scale of the suffering — more than 2 million South Sudanese have been displaced and about 3 million lack food — and the fact that much of the catastrophe was caused by a government we helped create. It’s not that the government is worse than the rebels, but I find it particularly offensive to see atrocities committed by those we backed.

I’ve known President Salva Kiir for years and rooted for him to succeed. But he and others in his government, with help from the rebels, risk destroying their country.

Kiir is now also cracking down on aid groups at a time when humanitarian workers are the only heroes here, struggling on even though 50 of them have been killed here since the latest civil war erupted just over two years ago.

A peace agreement reached last August is the last, best hope, but it hasn’t been fully implemented.

It’s time for an international arms embargo on South Sudan, and sanctions aimed at the assets of top leaders on both sides, while greater support is given to humanitarian organizations and efforts to protect civilians. South Sudan is running out of money, and that, too, should be used as leverage to force implementation of the peace accord.

If a country that the U.S. supported so strongly collapses into genocide because we didn’t do all we could, that will be part of the Obama legacy. Bravo to the U.N. secretary-general, Ban Ki-moon, for visiting the country a few days ago, because we need an international push to make the peace agreement stick and create real consequences for committing atrocities.

South Sudan is running out of time.