Complex sentence: The Ethiopian Civil War began on 12 September 1974 when the Marxist Derg staged a coup d'état against Emperor Haile Selassie, and lasted until the Ethiopian People's Revolutionary Democratic Front (EPRDF), a coalition of rebel groups, overthrew the government in 1991.
Split into simpler sentences: The Ethiopian Civil War began on 12 September 1974 when the Marxist Derg staged a coup d'état against Emperor Haile Selassie. The civil war lasted until the Ethiopian People's Revolutionary Democratic Front (EPRDF), a coalition of rebel groups, overthrew the government in 1991.