Eric Reeves is the author of “A Long Day’s Dying: Critical Moments in the Darfur Genocide.”

Sudan is once again at war with itself — or, more accurately, the ruthless regime in Khartoum is again waging war on peoples at the marginalized peripheries as a means of crushing growing rebellion. The primary target in this widespread conflict is not the people of Darfur, although they continue to languish amid ghastly violence and deprivation. No, these latest targets are the African people of the border regions between northern Sudan and the new Republic of South Sudan: the Nuba Mountains of South Kordofan and Blue Nile.

Last May, Khartoum’s military seized Abyei, a contested border region where Khartoum had refused to allow a promised referendum on self-determination in January 2011. The seizure displaced virtually the entire indigenous population of Dinka Ngok, more than 110,000 people, who fled to South Sudan, where they remain in poor conditions. Emboldened by the diffident international response to this assault, Khartoum moved in June against the rebels of South Kordofan and, more generally, the African Nuba people.

A bloodbath ensued in Kadugli, the state capital, and Nuba (who Khartoum claimed were “rebel sympathizers”) were relentlessly targeted in house-to-house searches and roadblocks reminiscent of Rwanda. Fighting has now moved to the central Nuba Mountains, where all humanitarian access has been denied by the regime in Khartoum, which continues merciless civilian bombings.

In September, the Sudanese government, still unchecked by international action, launched attacks on yet another region on the border, Blue Nile. Additional hundreds of thousands of civilians were displaced, many fleeing to neighboring Ethiopia or South Sudan. They’re in desperate condition, as are refugees from South Kordofan.

For more than seven months Khartoum has denied all international relief to both Blue Nile and South Kordofan, bringing more than half a million people to the brink of starvation. Famine-like conditions are expected by March; children are already dying from malnutrition. Food supplies are exhausted in both regions, with little hope on the horizon: Spring planting and fall harvesting of staple crops were disrupted by aerial attacks. The U.N. Food and Agriculture Organization predicts that the harvests will largely “fail.”

How is this President Obama’s war? What policy responsibility does he bear? In November 2010, his administration announced that it was “de-coupling” Darfur from bilateral negotiations over the issue of greatest strategic interest to Khartoum: its presence on the State Department list of terrorism-sponsoring nations. The decision was an unmistakable signal that Darfur was being “de-coupled” more broadly, which is precisely what occurred. At the same time, the administration pressured South Sudan to “compromise” further on Abyei. Since the South had already compromised repeatedly, this made clear to all parties that the United States had put expediency before principle in steering the 2005 Comprehensive Peace Agreement to completion, whatever the consequences for areas outside South Sudan.

The regime in Khartoum calculated, correctly, that with this recalibration of policy there would be no consequences for seizing Abyei. Attacks against civilians associated with rebel forces in South Kordofan began two weeks later, with compelling evidence of widespread atrocities against the Nuba. When the United States and other international actors failed to respond, Khartoum took note and moved on Blue Nile.

Great powers can be actively responsible for war, as in Iraq and Afghanistan, or passively responsible by acquiescing before ruthless militarism that threatens millions of civilian lives. In Sudan there is strong evidence that Obama — despite his rhetoric during the 2008 campaign — has no intention of playing anything but a passive role in responding to potentially cataclysmic human destruction. In a moment of supreme hypocrisy, Obama’s special envoy for Sudan, Princeton Lyman, said in December: “Frankly, we do not want to see the ouster of the [Sudanese] regime, nor regime change. We want to see the regime carrying out reform via constitutional democratic measures.”

The notion that Khartoum’s genocidal National Congress Party regime will “carry out reform via constitutional democratic measures” is both preposterous and painfully revealing of the administration’s disingenuousness. In the same vein, Obama administration officials have repeatedly declared that they will hold “accountable” those responsible for bombing attacks on civilians carried out by the regime’s military aircraft. In other words, the Obama administration insists upon “accountability” for those within the Khartoum regime — some of whom have been charged by the International Criminal Court with “crimes against humanity” — but nonetheless doesn’t wish to see “regime change.”

This is hopelessly self-contradictory and morally bankrupt — and from such bankruptcy are war and famine fashioned. Time is exceedingly short. The Obama administration must do what is necessary to secure agreement from Khartoum for humanitarian corridors to acutely distressed populations, presently targeted as a means of suppressing rebellion. If the regime balks, Obama must be prepared to compel, militarily, the opening of such corridors.