ADDIS ABABA, Ethiopia — Astebeha Tesfaye went to visit friends in Eritrea, and had to stay 20 years.

“I was going to take the bus the next day,” he said by phone on Tuesday, “but I heard that the roads were blocked, and that no one was going to move either to Eritrea or Ethiopia.”

Mr. Tesfaye was traveling as war broke out between Ethiopia and Eritrea, locking the two countries in hostilities that eventually left tens of thousands dead. Cross-border phone calls were banned, embassies were closed and flights were canceled. Travel between the countries became impossible.

But on Tuesday, the leaders of Ethiopia and Eritrea reopened crossing points on their shared border, clearing the way for trade between the two nations. The development was part of a series of reconciliation moves that began in July, when Prime Minister Abiy Ahmed of Ethiopia and President Isaias Afwerki of Eritrea signed a formal declaration of peace.