South Sudan on Tuesday accused Sudan of building up forces along their border, in a sign that efforts to set up a buffer zone between the neighbours and resume the oil exports vital to both economies have made no progress.
The two countries came close to war last April in the worst border clashes since South Sudan seceded in 2011 under a peace agreement that ended one of Africa's longest civil wars.
The dirt poor fighting the almost dirt poor. The war between Ethiopia and Eritrea more than a decade ago is a similar lesson.
Resting your confidence in peace on rational calculations of benefit and loss is not supported by history.