In a further affirmation of a breakthrough agreement to end one of Africa’s most enduring conflicts, an airplane from Ethiopian Airlines flew on Wednesday to neighboring Eritrea across a frontier that had once been a front line in two decades of deep, mutual hostility.

Flight 312 left Addis Ababa, the Ethiopian capital, at 9 a.m. local time, for Asmara, the capital of Eritrea, just nine days after the two countries announced the formal end of the “state of war” that followed a bloody conflict over their shared border. The war raged from 1998 to 2000 and claimed 80,000 lives, but a peace deal was never fully implemented.

The newest agreement, announced on July 9, has been depicted by analysts as the harbinger of an unfamiliar stability — or renewed volatility — in the Horn of Africa, a region known for seemingly intractable disputes stretching back to the Cold War era.

Eritrea, for instance, fought a decades-long struggle against Ethiopian dominance and annexation to secure independence in 1993. Five years later, war between Ethiopia and Eritrea, a former Italian colony, broke out over the delineation of their shared border.