In this April 29 photo, South Sudan's then-First Vice President, Riek Machar, left, and President Salva Kiir in the capital, Juba. (Jason Patinkin/Associated Press)

THE RESULTS of a two-year investigation into kleptocracy in South Sudan, published this month by a group called the Sentry, lifts the veil on widespread plundering of the young nation by its leaders. The investigation found that family members of top officials often live abroad in multimillion-dollar mansions, stay in five-star hotels, reap the benefits of shady deals and drive luxury cars while the country suffers from the brutal aftermath of civil war and widespread near-famine conditions. The report also shows that the kleptocracy depends on a network of lawyers, banks and arms brokers who facilitate the pillaging.

Make no mistake, the problems in South Sudan would be formidable even with enlightened leadership. But the fact is that the misery of the past few years — civil war, human rights atrocities, massive flight and internal displacement, sexual violence and widespread theft from state coffers — has been inflicted by President Salva Kiir and his rival and former first vice president, Riek Machar, and their supporters. This is a top-down disaster. The Sentry report suggests that not only ethnic rivalry divides Mr. Kiir and Mr. Machar, but also corruption and greed aggravated the tension.

Here’s the rub: The leaders of South Sudan, starting with Mr. Kiir, may lack the willpower to improve life for citizens — but they can certainly make it a lot worse. The tricky part will be holding them accountable while not impeding the flow of desperately needed humanitarian relief. The United Nations now estimates that more than 1 million refugees have fled South Sudan since the civil war began in December 2013.

The civil war was patched up in a peace agreement calling for a transitional government, but Mr. Machar recently fled South Sudan amid fresh instability and violence. Mr. Kiir is well on the road to despotism, cracking down on civil society and media. There are reports of a new campaign by government commanders to recruit child soldiers. On July 11, 50 to 100 armed men, who have been identified as government forces, entered the Terrain Camp residential compound in the capital, Juba, where foreign aid workers lived, and went on a rampage, robbing, beating and sexually assaulting them. A well-respected South Sudanese journalist was killed.

The United States played a critical role in South Sudan’s independence, but Mr. Kiir no longer seems to be listening to Washington. The situation should not lead to complacency. A point of the Sentry report is that further sanctions would threaten the kleptocrats. Separately, the United Nations Security Council has proposed a protective force of 4,000 troops on top of the 12,000 already there, but Mr. Kiir may not accept it. If the new force is obstructed, it will trigger an arms embargo, long threatened and overdue.

Five years ago, then-Secretary of State Hillary Clinton celebrated South Sudan’s independence on these pages, saying it was a moment of “a new national identity and new national promise.” Now, it is clear South Sudan’s leaders have proved ruinous. That sound coming from Washington is one long, deep sigh of disenchantment.