Before the 16th century, Somali sub-groups moved from coastal regions such as Zeyla, Berbera, and Mogadishu to the interior of the Horn of Africa, settling in present-day Ethiopia and Somalia. They were actively involved in the Sultanate of Adal’s military campaigns against the Christian highland kingdom and some Somali pastoralists relocated to the eastern highlands in search of water and pasture during these conflicts.

The Afar people have long inhabited northeastern Ethiopia, Djibouti, and southeastern Eritrea. Facing drought and famine before the 16th century, they moved towards the middle Awash. During the conflicts between Sultanates and the Christian kingdom, the Afar moved to avoid warfare, aligning with Sultanate forces and later engaging in conflicts in the Ethiopian highlands.

The Argoba, an ancient group with early Islamic influences, were significant in trade and the formation of Muslim states. Their strategic location along trade routes and conflict zones facilitated their spread across Southern Wollo, Harar, and surrounding areas. Today, they are present in the Argoba Zone of the Afar Regional State and various other regions.

The Oromo population movement in the 16th century, originating from the Bale highlands, was driven by overpopulation and pasture shortages. They expanded significantly into central, southeastern, western, southern, and northern Ethiopia. Organized into two main confederacies—Borana and Barantu—the Oromo’s expansion led to the decline of medieval kingdoms and the Sultanate of Adal. They integrated new communities through the Moggassa (mass adoption) and Guddifacha (individual adoption) systems, which bolstered their military and economic power. Despite the decline of the Gadaa system, a traditional democratic institution, it remains a significant historical example of democratic governance.