There were several different Christian states that operated in territory now occupied by Ethiopia, but the most famous was Abyssinia.
The Indian ocean lies to the east of Africa,
The "horn of Africa" got its name form the horn-shaped figure at the east of Africa. The east coast of Africa is shaped like a horned animal, like a rhino.
The term East Africa is a proper (compound) noun, the name of a specific place.
Kingdom of Mali
Portuguese East Africa
The Indian Ocean.
Kenya
nigeria
china
Tanzania
maputo
The Indian Ocean people