NAIROBI, Sept. 26 -- Five days before Ethiopian and Tigrayan forces exchanged fire this week, seven armed groups that spent much of the last decade trying to kill each other stood behind a single announcement instead.

The Ethiopian Peoples' Forces Alliance for Survival brings together the Tigray People's Liberation Front and the Amhara Fano National Movement, forces that fought on opposite sides of the 2020-2022 civil war that killed roughly 600,000 people, alongside the Oromo Liberation Army, the Ogaden National Liberation Front, and armed movements from the Afar, Benishangul and Gumuz regions. Their stated goal is to remove Prime Minister Abiy Ahmed's government and install a transitional administration. Their first joint action came a...