A General History of Ethiopia

Ethiopia’s history as an organized and independent polity dates back to about 100 BC with a kingdom at Axum in the Northern Regional state (Killil) of Tigray.
But the Axumite kingdom as a state, emerged at about the beginning of the Christian era, i.e.,4th A.D and flourished during the succeeding six or seven centuries. It then underwent prolonged decline from the eighth to the twelfth century A.D. Axum’s period of greatest power lasted from the 4th  through the 6th centuries .Its core area lay in the highlands of what’s today southern Eritrea, Tigray, Lasta (in the present-day Wallo), and Angot (also in Wallo); its major centers were at Axum and Adulis. Earlier centers, such as Yeha, also contributed to its growth. At the kingdom's height, its rulers over the Red sea coast from Sawak in present day Sudan, in the North to Berbera in the present-day Somalia and inland as far as the Nile valley in modern Sudan. On the Arabian side of the Red sea, the Axumite rulers at times controlled the Coast and much of the interior of modern Yemen. During the sixth and seventh centuries, the Axumite state lost its possessions in South West Arabia and much of its Red sea coast line and gradually shrank to its core area, with the political center of the state shifting farther and farther Southward.
The rise of Islam in the Arabian Peninsula had a significant impact on Axum kingdom during the seventh and eighth centuries .By the time of the Prophet Mohammed’s death (A.D.632), the Arabian Peninsula, and thus the entire opposite shore of the Red sea, had come under the influence of the new religion. The steady advance of the faith of Mohammed through the next century resulted in Islamic conquest of all of the former Sassanian Empire and most of the former Byzantine domination.