Members of the White Army, a South Sudanese anti-government militia, attend a rally in Nasir on April 14, 2014. (Zacharias Abubeker/AFP/Getty Images)

THE SPECTACLE of failure in South Sudan is saddening. A nation that was brought to independence with the enthusiastic support of the United States, ending a long civil war, is now being torn apart by its own leaders. Millions in South Sudan are enduring hunger and disease. In the annals of nation-building experiments, this one may be remembered as ill-fated and short-lived. President Obama is now threatening further punishment of warring parties in a nation he once helped to its feet.

The president’s meeting in Addis Ababa, Ethi­o­pia, on Monday with leaders of Uganda, Sudan, Kenya, Ethiopia and the African Union was more like a gathering of surgeons pondering one last rescue for a patient on the road to doom — one who refuses to be saved. The regional leaders have backed opposing sides in the civil war. Mr. Obama urged them to make one last attempt to persuade their allies inside South Sudan to stop fighting, but the tone was grim. Every previous attempt at peace over the past 19 months has failed, and expectations are not high. A senior administration official told reporters that the civil war is “a classic case of venal leaders squandering a huge opportunity that they themselves earned, that we all in the international community supported them to obtain. So we can’t undo this for them. They’ve got to fix this.”

South Sudan’s president, Salva Kiir, and his one-time deputy and now mortal rival, Riek Machar, deserve the largest share of blame for wrecking their nascent nation. The African Union has now delivered to the government in Juba the report of a commission of inquiry that documents grave human rights abuses in the conflict. This report ought to be made public and the perpetrators brought to justice. A corruption watchdog group, the Sentry, chronicles in a new report how South Sudan has been destroyed from within by “a kleptocratic regime” of self-interested elites who have siphoned off its national wealth. The fighting chiefs in South Sudan may not appreciate how the goodwill they once enjoyed in the United States has vanished.

It is unfortunate that Mr. Obama remained aloof from the downward spiral for so long, but there was value in his personal warning in Addis Ababa that “we don’t have time to wait” and his threat of tougher measures if there is not an agreement, through an expanded peace effort, in the coming weeks. So far, threats of punishment have done little to deter the combatants. This time probably won’t be different. It may be hard for the United States to discipline the leaders of South Sudan after all that went into the quest for independence; many officials of the present administration invested heavily in hopes for the new country. But they must end the hand-wringing. In order to save the people of South Sudan from further misery and suffering, it is time to impose an arms embargo, travel bans and much stronger sanctions aimed squarely at the individuals responsible for the horrors.