Axum (or Aksum), the greatest power in Africa, after the Roman Empire – a quick view

The ancient kingdom of Axum (also called Abyssina) that stretched westward to the valley of the Nile and southward to the Somali coast, in what is today northern Ethiopia. Its capital city was also called Axum. Its port of Adulis, on the Red Sea, was a market for African slaves, ivory, papyrus, and gold, as well as spices from India. Like Byzantium, it minted gold coins, and had a sophisticated court where Greek was spoken. Its economic and diplomatic influence extended to Arabia and Persia. Christianity was probably established during the fourth century, perhaps during the reign of king Ezana. Its Monophysite church was dependent on the patriarch of Alexandria. Justin I persuaded king Elesboam to invade Himyar, i.e., southern Arabia (Yemen), in 525, to counteract any Persian attempt to control the area. In 531, Justinian I sent an embassy to Axum to persuade the Ethiopians to destroy the Persian silk trade by transporting silk between Ceylon and the Red Sea ports. However, nothing came of this scheme. In the seventh centuries, Axum lost its Red Sea ports to the Arabs, precipitating its decline. However, from the fourth to the seventh centuries, Axum was the greatest power in Africa after Byzantium.

(Source: «Historical Dictionary of Byzantium», by John H. Rosser)

Despite common belief to the contrary, Aksum did not originate from one of the Semitic Sabaean kingdoms of southern Arabia but instead developed as a local power. At its apogee (3rd–6th century CE), Aksum became the greatest market of northeastern Africa; its merchants traded as far as Alexandria and beyond the Nile River. Aksum continued to dominate the Red Sea coast until the end of the 9th century, exercising its influence from the shores of the Gulf of Aden to Zeila on the northern coast of Somaliland (modern Somalia and Djibouti).

During the 2nd and 3rd centuries CE its growth as a trading empire increasingly impinged on the power of the kingdom of Meroe, the fall of which was brought about in the 4th century by an Aksumite invasion. During the 4th century the kings of Aksum were Christianized—thus becoming both politically and religiously linked to Byzantine Egypt. At the same time, they extended their authority into southern Arabia. In the 6th century an Aksumite king reduced the Yemen to a state of vassalage. In the latter part of the 6th century, however, the Persians invaded South Arabia and brought Aksumite influence there to a close. Later the Mediterranean trade of Aksum was ended by the encroachment of the Arabs in the 7th and 8th centuries.

Gradually, Aksumite power shifted internally to the Agau (Agaw, or Agew) people, whose princes shaped a new Christian line in the Zagwe dynasty of the 12th–13th century.

(Source: https://www.britannica.com/place/Aksum-ancient-kingdom-Africa)