The successful creation of the Republic of South Sudan on 9 July was an enormous achievement. But just weeks after the split, the relationship between the two is disintegrating.

In the all-out effort to ensure the secession process was peacefully fulfilled, crucial elements of the 2005 Comprehensive Peace Agreement were neglected. The referendum on the future of the border town of Abyei fell by the wayside, the management of the popular consultations in the northern border states of Blue Nile and South Kordofan was never properly addressed, and post-independence economic arrangements were never made.

These failings are now coming back to haunt those involved. In May, 20,000 people were forced to flee the North’s army as it marched into Abyei, and more than 73,000 people have been internally displaced by clashes in South Kordofan. Local observers have warned that if fighting is not contained, civil war could start to spread once more through a territory that for the past 50 years has known little else.

Negotiations on the management of Sudan’s $39bn international debt and the sharing of oil resources, the lifeblood of the economy of both states, are meanwhile showing no signs of progress, and the early introduction of a new South Sudanese currency is already causing resentment in Khartoum.

From a political and historical point of view, the abrasiveness of the relationship is understandable. From an economic perspective, it is nonsense. The two countries are so mutually reliant that the case for peace is overwhelming. Continuing conflict serves neither state and nor does obstinacy at the negotiating table.

That the South’s secession was able to take place at all was due in equal part to the will to make it happen in Juba, the forbearance to allow it to happen in Khartoum, and the commitment of the international community to mediate.

The time has come for the two Sudans to take responsibility for their own future, and to turn a destructive relationship into a symbiotic one.