Eritrea is a country of nine nationalities. They belong to Nilo-Saharan, Kushitic, and Semitic families. The earliest inhabitants of Eritrea were Pygmoid type of people. The Nilo-Saharan family (Nilotic) were the first migrants to Eritrea. They migrated to Eritrea from Upper Nile. They intermarried with the Pygmoid population. This resulted in Nara and Kunama ethnic groups.
During 2000 BC Kushites migrated to Eritrea from North Africa. They intermarried with the earlier inhabitants. These are represented by the Beja (Ben Amir and Hidareb), Bilen, Afar and Saho. The latest migrants were the Semitic people (1000BC-700 BC). They came across the Red Sea from the firtile agricultural highlands of the Arabian Peninsula. First they settled on the coastal areas. But they found the coastal areas to be hot and arid compared to their original land. So they encroached into the cooler and fertile highlands of Eritrea. Therefore the Eritrean people can be grouped into three. These are: Nilotic group-Nara and Kunama, Kushitic group-Saho, Afar, Bilen, Beja (Ben Amir and Hidareb, and the Semitic group, Tigre, Tigrigna and Rashaida.
The Semitic group had an immense influence on military, political, economic and social cultural life in the Eritrean society. They introduced domestic animals (camels, horses, sheep), irrigation farming, new agricultural seeds, construction of houses, handcraft (pottery, woodwork, weaving), writing, trade, and mining. Moreover, people started to organize themselves to live together in villages under one chief. The villages evolved into city-states. This is how the Axumite Kingdom emerged.
Source: New World History Outline