1974年9月，由於一批少壯軍官組成”軍隊、警察和地方軍協調委員會"(即DERGUE,英文SHADOW之意，後泛指軍政府和門格斯圖政權)發動軍事政變，推翻海爾·塞拉西政府，宣佈結束帝製，成立”臨時軍政府”。11月，”臨時軍政府”又改為"臨時軍事行政委員會"。12月，"臨時軍事行政委員會"宣佈埃塞俄比亞為"社會主義國傢",實行土地、金融財政機構和工業國有化。
Lt. Col. Mengistu Haile Mariam assumed power as head of state and Derg chairman, after having his two predecessors killed, as well as tens of thousands of other suspected opponents. The new Marxist government undertook socialist reforms, including nationalisation of landlords' and church's property. Before the coup, Ethiopian peasants' way of life was thoroughly influenced by the church teachings; 280 days a year are religious feasts or days of rest. Mengistu's years in office were marked by a totalitarian-style government and the country's massive militarization, financed by the Soviet Union and the Eastern Bloc, and assisted by Cuba. In December 1976, an Ethiopian delegation in Moscow signed a military assistance agreement with the Soviet Union. The following April, Ethiopia abrogated its military assistance agreement with the United States and expelled the American military missions.