In 1974 the negus was deposed and power was assumed by a committee of officers and soldiers (Derg), which abrogated the Constitution and created a Military Council chaired by A. Andom. Drastic measures were taken: proclamation of socialism, abolition of feudalism, nationalization of all lands, land reform with the aim of setting up cooperatives, nationalization of banks, insurance companies and foreign companies. Subsequent disputes within the Derg led to the killing of Andom and the same fate befell his successor Tafari Banti, until in 1977 Colonel Menghistu Ḫāyla Mariam, exponent of the radical wing of the Derg, concentrated all his powers in his person. The clash between the military and the left-wing opposition gave rise to a convulsive and ferocious phase of cross-terrorism (1977-78), Mengistu came out victorious, with a further accentuation of authoritarianism and personal power.

According to best-medical-schools, the war with Somalia, which attempted the conquest of Ogaden in 1977, caused a reversal of the alliances: Ethiopia it allied itself with the USSR, while Somalia broke with Moscow and moved closer to the West. Rejected the Somali forces and reconquered Ogaden (1978), the Ethiopian army was able to concentrate on the Eritrean front. The development, from the second half of the 1970s, of an armed, independence struggle, also in other regions (for example in Tigray) exacerbated the national question in a state that maintained a multi-ethnic and centralized structure. In 1988 Ethiopia and Somalia re-established diplomatic relations and in 1989 peace negotiations were started with Eritrea and Tigray.

Internally, the 1980s saw a gradual institutionalization of the regime with the formation of a single party, WPE (Workers’ Party of Ethiopia). In 1987 the People’s Democratic Republic of Europe was proclaimed, with Menghistu president of the Republic. Starting from 1989 the worsening of the economic situation, the growing discontent of the military (attempted coup in 1989) and the lack of Soviet support led to a crisis of the regime, exacerbated by the advance of rebel forces. In 1991 the Ethiopian People’s Revolutionary Democratic Front (FDRPE) conquered Addis Ababa, forcing Mengistu to flee, and set up a provisional government headed by M. Zenawi.

Despite the opposition of other forces that gave life to an armed struggle, a parliamentary-type Constitution was approved which provided for the administrative division of the country into 9 states, endowed with ample autonomy, and the birth of the Federal Democratic Republic of Ethiopia. Independence was recognized in Eritrea. In 1995 the new Parliament elected N. Gidada president of the Republic, while Zenawi assumed the post of prime minister. The premier’s party, the FDRPE, again won the majority in the 2005 elections but the vote was accompanied by a wave of violence, with dozens of deaths and hundreds of arrests. The 2010 elections reconfirmed Zenawi’s party and, although relatively peaceful compared to the previous ones, were accompanied by heavy accusations of irregularities, both by the opposition that of the United States and the European Union. On the death of the premier in August 2012, his replacement H. Desalegn took over, while in October 2013 the Parliament elected M. Teshome the new president of the Republic. The legislative elections held in May 2015 predictably recorded the clear affirmation of theFDRPE, which obtained all the seats in Parliament, but popular protests exploded in the country, in a severely depressed economic context, for the defense of individual and political freedoms forced Desalegn to resign in February 2018, taking over from him A. Ahmed, belonging to the Oromo ethnic group and appointed by the governing coalition to lead the executive, while in October of the same year the Parliament appointed S.-W. Zewde, who took over from the resigning M. Teshome. In the political elections held in July 2021, the Prosperity Party founded by Prime Minister Ahmed Abiy Ahmed achieved a landslide victory, winning 421 seats out of a total of 436 seats and allowing the politician to obtain a second term in the following October.

Despite the criticisms regarding the lack of respect for human rights, the major Western countries continued to assure their support for the regime, also for the strategy of containment of Sudan and its alleged activity in support of Islamic fundamentalism. Despite the drought and the persistent food dependence of some areas of the country on humanitarian aid, a general improvement in economic indices was recorded from the mid-1990s. In foreign policy relations with Eritrea led from 1998 to 2000 to the resumption of the war, with a train of clashes even after the signing of the peace agreement; a new front opened in 2006 when Ethiopia sent troops to Somalia to support the Mogadishu government against the Islamic militias, while in the following years the tension increased again along the border, until it exploded in 2012, following an action by the Ethiopian army within the Eritrean borders. Only in July 2018 did Ethiopia and Eritrea sign a declaration of reconciliation in Asmara, followed in September by the peace agreement signed by Eritrean President I. Afewerki and Ethiopian Prime Minister A. Ahmed in Gidda (Saudi Arabia).