For a long time, Sudan had been the “bete noire” of humanitarian activists. The government in Khartoum provided shelter to Osama bin Laden before American pressure mounted to such a level that he had to be invited to relocate to Afghanistan. It waged a grisly war in the western province of Darfur. This earned Sudan widespread condemnation for “genocide.” Then it ramped-up a smoldering conflict between the Muslim north and the Christian/Animist South Sudan. Eventually, the United States played a leading role in achieving national independence for South Sudan in July 2011.
This arguably marked a considerable success for the foreign policy of President Barack Obama. One question is whether it caused American diplomats to become too invested in that apparent success to see the possible flaws and even to correctly judge the character of the men who took power. They owed their positions in part—but only in part—to American diplomacy.
Immediately, a problem arose: South Sudan wasn’t a “nation”; it was an agglomeration of tribes. The two chief tribes were the Dinka and the Nuer. Although bitter hostilities had pitted Dinka against Nuer in the past, the two groups united to fight the government of Sudan. At independence, Salva Kiir, a Dinka leader became president, and Riek Machar, a Nuer leader, became vice-president.
Neither peace nor unity lasted very long. First, Riek Machar lost his position as vice-president. Then, in December 2013 civil war broke out between the Dinka and the Nuer. Many people perished in the fighting. The United Nations brokered a series of peace agreements that were honored only in the breach by the warring parties. Deaths have mounted into the tens of thousands. Generally, the Western press and humanitarian groups, like Amnesty International and Human Rights Watch, presented ample evidence of the mass killings to the Western public. Generally, that public showed no interest in these events.
That left it to governments to decide what course to follow, then to make the case for their policies to the voting public. Here the wheels came off American diplomacy. Although the Obama administration had played an important role in creating the South Sudan, it failed to engage with the subsequent crisis. By Summer 2014, humanitarian groups were urging the United States to use an arms embargo and targeted economic sanctions (of the sort rapidly applied to Russia after it re-took the Crimea from Ukraine) to try to restrain the killing. However, division ruled in the American government.
In Summer 2016, the United States urged the U.N. to authorize the sending of 4,000 additional peace-keeping troops to the capital city of Juba. In September 2016, the American ambassador to the U.N., Samantha Power, got the government of South Sudan to agree to admit additional peace-keeping troops. It appears that President Kiir only agreed to this to get Power to go back to Washington. So, far none have actually been allowed into the country.
By November 2016, with the Obama administration headed for the exits, Power finally won support within the government for an American proposal to the U.N. to impose both economic sanctions and an arms embargo. In late December 2016, the U.N. Security Council rejected this proposal.
Why? Perhaps because the Russians opposed sanctions, and African countries didn’t want to impose sanctions. Perhaps because it is safe to defy an outgoing administration.
 Somini Sengupta, “Failures on South Sudan Highlight the Limits of U.S. Diplomacy,” NYT, 19 January 2017.
 And not just for foreign countries. This is the second recent article implicitly critical of Samantha Power as more theatrical than effective. See: Helene Cooper, “From a Fateful Motorcade,..,” NYT, 6 January 2017.