With Secretary of State John Kerry traveling to Ethiopia today, site of the peace talks for South Sudan, he will be greeted by a bracing reality: no civilians in the world are in greater danger than those of South Sudan. Not in Syria, Central African Republic, or Darfur is the threat of targeting on the basis of identity so immediate as it is for certain ethnic groups in vulnerable areas of South Sudan. Given the lack of protection by Juba government forces, the inability of UN troops to protect large numbers of people, and the absence of significantly greater protection from the broader international community, hundreds of thousands of people are likely to die in the coming months, whether directly through targeted violence or indirectly through hunger. It is an unsurpassably urgent crisis and yet the world's response has been in no way comparable to the threats civilians now face on a daily basis.

Following the political and military events of mid-December when targeted violence erupted in Juba, capital of South Sudan, conflict has steadily escalated. Now, more than four months later, we are witnessing events that have all the hallmarks of genocide. The split in South Sudan's army—the Sudan People's Liberation Army (SPLA)—has been largely along ethnic lines, primarily between the Dinka, the largest tribal group in the South, and the Nuer, the second largest tribal group. As a consequence of this split, what appeared initially to be a vehement demand for governance reforms—but without evident military goals—has developed into a full-scale military rebellion, with violence escalating into something like "symmetric warfare" between two forces that are comparably trained and armed.

Unlike the "asymmetric warfare" to which we have become accustomed to hearing about (e.g., Iraq, Afghanistan, Darfur), symmetric warfare ensures heavy casualties in military confrontations. But victories and defeats now have more ominous consequences; for in South Sudan the victors see military victory as justifying civilian slaughter of the predominant ethnic group of the opposing forces. And with a terrifying momentum, ethnic slaughter leads to yet greater ethnic slaughter. When the town of Bentiu in oil-rich Unity State fell to rebel forces on April 15-16, hundreds of Dinka civilians (and many Darfuris) were hunted down and killed—men, women, and children. Hate radio locally broadcast locally urged the rape and murder of Dinkas—or even Nuer who were not enthusiastic enough about the victory. Meanwhile, in Bor (Jonglei State), Nuer civilians under the protection of the UN force (UNMISS, UN Mission in South Sudan) made the mistake of celebrating the victory of the rebels in Bentiu; in reprisal, a large gang of Dinka youth broke into the UN compound and killed dozens of Nuer. We have seen earlier versions of this vicious ethnic violence in Malakal (Upper Nile) and in other smaller towns, as well as Juba itself.

Toby Lanzer, who heads UN humanitarian operations in South Sudan, has referred to the slaughter in Bentiu as a "game changer." Whether or not the game changed with this particular incident, it provided clear evidence that without an international force capable of enforcing a separation of armed elements, or at least robustly protecting civilians, the fighting will intensify and become more relentlessly ethnic in character.

Beyond the human suffering and destruction that is a consequence of this terrible violence, an even larger threat looms. For fighting has already displaced more than a million people from their homes and villages, and has done so in the midst of the planting season—April and May, when the rainy season begins. For planting to be successful, people, seeds, and farming equipment need to be in the same place at the same time. For displaced people this simply doesn't happen; and if this planting season is a failure, the fall harvest will be as well. Famine will stalk the land and as many as seven million people will confront extreme food insecurity—in short, starvation. And the penchant that both parties have for blocking humanitarian aid to areas controlled by the other will exacerbate the difficulties for residents of the most affected areas.

The situation, however, is not hopeless. There are steps that could be taken to prevent full-scale genocide, which Secretary Kerry can advance during his visit. First, appropriate international forces need to be deployed to South Sudan to protect civilians. A vanguard regional force should deploy to protect large concentrations of internally displaced persons who are most at risk of targeted attack. This must be followed by a substantial augmentation of the UN mission in the region (UNMISS), which as it has deployed is militarily incapable of protecting all civilians in need.

Second, a major international diplomatic press led by a respected international figure is needed to negotiate a cross-line humanitarian assistance delivery channel.

Third, biting sanctions need to be imposed by a coalition of states willing to collectively seize bank accounts, houses, cars, and any other assets owned by government or rebel officials—or other regional actors—complicit in war crimes or obstruction of aid deliveries. Consequences are needed to increase international leverage over the parties, including ramping up efforts to create a mixed judicial process internally and to refer the war crimes perpetrated there to the International Criminal Court

Fourth, international efforts in support of a peace process must redouble. Leverage should be built by key states with influence and deployed in the service of the talks. And civil society and political opposition should receive greater international support and be meaningfully included in the peace process as well.

Twenty years ago Rwanda was engulfed in the flames of hatred, as Darfur has been for 10 years. Hundreds of thousands died because no meaningful international action was taken. With South Sudan threatening to explode in an ever-expanding cycle of revenge, that legacy of international failure must be reversed, or hundreds of thousands more will die—on our watch.

Eric Reeves is a professor at Smith College in Northampton, Massachusetts. His most recent book on Sudan is Compromising With Evil: An archival history of greater Sudan, 2007 – 2012.

John Prendergast is co-founder of the Enough Project, an initiative to end genocide and crimes against humanity affiliated with the Center for American Progress.