Here is the Genesis of the Cuban-Ethiopian relations. Many Ethiopians mistakenly think that Castro helped free Ethiopia from Somalia occupation.
The truth of the matter is the Soviet Union wanted to dominate Africa and find a way to strangle trade on the Red Sea and the Gulf of Aden. The Russians used Somalia to destabilize East Africa since 1961 and pressure the king to allow USSR into the region. The King refused and he paid for it with his life.
The King of Ethiopia was overthrown in a violent revolution in 1974. The Somalia’s having planned to create Greater Somalia by annexing Ogaden did not want to deviate from their plan. Castro even went to Mogadishu in early 1975 to persuade Siad Barre to change his mind about invading Ethiopia. Siad Barre did not care or bother to listen to the Russians or Cuba and went ahead with his original plan to invade Ethiopia. When Ethiopia was totally invaded to the tune of Somalians showing up in Dire Dawa at the end of 1975, the Cubans changed side and decided to fight with Ethiopians against their former allies the Somalis. Castro, from a small unsuccessful communist Caribbean Island, was only paying his heavy debt to USSR by acting as a mercenary for USSR interest. He had no means or desire to help a poor African country. Attached is a document that was prepared as a thesis by Lieutenant Kessler in 1991.
The Ogaden War was a conflict between Somalia and Ethiopia between 1977 and 1978. Fighting erupted in the Ogaden region as Somalia attempted to liberate the area. The conflict ended with a Somali retreat.
When the Soviet Union began to support the Ethiopian Derg government instead of the Somali government, other Communist nations followed. The Cuban Militarydeployed 15,000 combat troops along with aircraft to support the Derg government and the USSR military advisers in the region.
Cubans trained Eritreans but later, in a political reversal, trained Ethiopian Marxist forces who were fighting against Eritreans.