The Indian ocean lies to the east of Africa,
The mythical Christian king is known as Prester John. He was believed to be a powerful and wealthy ruler of a Christian kingdom in Africa or Asia during the Middle Ages. Legends about Prester John inspired many European explorers and adventurers in their quests for new lands and the spread of Christianity. His kingdom was often depicted as a fantastical place filled with riches and wonders.
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
nigeria
Kenya
The Indian Ocean.
Tanzania
china
Portuguese East Africa
The name of the mass of East African land that juts out into the Indian Ocean is the Horn of Africa.