The Abyssinian-Adal war was a military conflict between the Ethiopian Empire and the Adal Sultanate that took place from 1529 until 1543. Abyssinian troops consisted of Amhara, Tigrayan and Agew ethnic groups. Adal forces consisted mostly of Afar, Somali, Harla, Argobba, Arab, formations supported by the Ottoman.
Between 1529 and 1543, the military leader Imam Ahmad ibn Ibrahim al-Ghazi defeated several Ethiopian emperors and embarked on a conquest referred to as the Futuh Al-Habash ("Conquest of Abyssinia"), which brought three-quarters of Christian Abyssinia under the power of the Muslim Sultanate of Adal. With an army mainly composed of Somalis, Al-Ghazi's forces and their Ottoman allies came close to extinguishing the ancient Ethiopian kingdom. However, the Abyssinians managed to secure the assistance of Cristovao da Gama's Portuguese troops and maintain their domain's autonomy. Both polities in the process exhausted their resources and manpower, which resulted in the contraction of both powers and changed regional dynamics for centuries to come. Many historians trace the origins of hostile Ethiopia–Somalia relations to this war. Some scholars also argue that this conflict proved, through their use on both sides, the value of firearms such as the matchlock musket, cannons and the arquebus over traditional weapons.
The victories that gave the followers of Imam Ahmad the upper hand came in 1531. The first was at Antukyah, where cannon fire at the start of the battle panicked the Ethiopian soldiers. The second was on 28 October at Amba Sel, when troops under the Imam not only defeated but dispersed the Ethiopian army and captured items of the Imperial regalia. These victories allowed the army to enter the Ethiopian highlands, where they began to sack and burn numerous churches, including Atronsa Maryam, where the remains of several Emperors had been interred. The country was looted by the Ahmad's forces, who destroyed several Christian monuments and oppressed the non-Muslim Amhara and Tigray.
Mohammed Hassan has plausibly argued that because the participants in this conflict weakened each other severely, this provided an opportunity for the Oromo people to migrate into the lands south of the Abay east to Harar and establishing new territories.