It is still, barely, not too late for the two Sudans to avoid full-scale war. But it's not easy to be optimistic.
The two Sudans can still avert a war, but instability is certain
Less than a year has passed since the independence of South Sudan in July 2011. Already, the euphoria of statehood has been replaced by the uncertainty of a widening conflict between the new nation and its neighbour to the north, the Republic of Sudan.
What was a war of words between Khartoum and Juba has become an escalating series of retaliations. In recent months, Khartoum has commandeered Juba's oil, leading South Sudan to cease oil production entirely. Khartoum's air force has bombed towns and villages in South Sudan's Unity state. At least one Sudanese military aircraft has been downed. Last week, South Sudan's army crossed the de facto, if not de jure, international border into the oilfields of Heglig.
Conflict is not confined to the immediate border. The incomplete implementation of commitments made to the peoples of Blue Nile, South Kordofan's Nuba Mountains and Abyei always jeopardised the prospect of a lasting peace between the two Sudans.
Fighting in Blue Nile and South Kordofan continues, not as proxy wars between north and south, but as legitimate local grievances with their own structural causes and solutions. The war in the Nuba Mountains has been particularly vicious. Neither the Nuba rebels nor the government in Khartoum are in the mood to compromise. And at best, Khartoum is indifferent to humanitarian suffering in Nuba areas.
For Sudan, this is governance as usual. For those hoping that South Sudan's independence dividend might have paid out a bit longer, there is disappointment if not surprise. The economies of both states have suffered serious damage. The Sudanese pound has hit record lows. With no oil money coming in, South Sudan has imposed a drastic austerity budget. Both states feel compelled to protect military spending, which inevitably means that other government budget lines suffer.
For both Sudans, there is an apt warning in the experience of Eritrea, the only other African country to become independent in recent years. Eritrea seceded from Ethiopia in 1993. By 1998 it was embroiled in a border conflict with Ethiopia, centred on the town of Badme. Tens of thousands of soldiers lost their lives in pointless trench warfare. A generation of antagonism and violence between the two states has followed.
South Sudan is well aware of this history. In his inaugural speech at South Sudan's independence day celebrations, South Sudanese president Salva Kiir made time to include this plea: "I would like to strongly urge my brothers in Ethiopia and Eritrea to find a peaceful way to resolve their differences."
This does not have to be Sudan and South Sudan's Badme moment. Military casualties on both sides have been relatively few. Neither army can or will fight a trench war. The situation in Abyei is reminiscent of Ethiopia's failure to implement an international tribunal's ruling to cede Badme to Eritrea. Abyei also is a territory subject to multiple international rulings, and whose final status remains unresolved, largely due to Khartoum's intransigence. But the situation is not the same: a full-scale war between Sudan and South Sudan can still be avoided.
Avoiding another generation of acrimony between north and south is another matter. History is not encouraging. There has been far more war than peace in the historic Sudan. It is all too easy to predict a future of conflict and instability. It is also easier to escalate the situation than to show restraint. Brinkmanship is an old tradition of Sudanese politics. And current politics have not moved beyond a zero-sum game.
In sending its troops into Heglig, South Sudan may well have overreached. Swift condemnation from the African Union and the United Nations has put pressure on South Sudan to withdraw its forces. In contrast, international actors have practically no leverage over Khartoum to cease hostilities in South Kordofan and offensive aerial sorties over South Sudan.
In that same July speech, Mr Kiir also said: "Notwithstanding decades of war and suffering, the people of South Sudan do not harbour any bitterness towards our erstwhile compatriots. Our people, by their attitude and actions will demonstrate to our Sudanese brothers and sisters and to all our neighbours that we are indeed their partners in peace - committed to the principles of good neighbourliness."
All those who wish for peace in Sudan and South Sudan hope that those sentiments return, on both sides of the border. Continuing violent escalation in the borderlands is the immediate threat. But long term instability will damage South Sudan's birthright and could ruin the lives and livelihoods of millions more.
Aly Verjee is senior researcher at the Rift Valley Institute, a non-profit research and training organisation working in East Africa