Under the Emperors Theodore II (1855-68), Johannes IV (1872-89), and Menelik II (1889-1913), the kingdom was consolidated and began to emerge from its medieval isolation. When Menelik II died, his grandson, Lij Iyassu, succeeded to the throne but soon lost support because of his Muslim ties. The Christian nobility deposed him in 1916, and Menelik's daughter, Zewditu, was made empress. Her cousin, Ras Tafari Makonnen (1892-1975), was made regent and successor to the throne. In 1930, after the empress died, the regent, adopting the throne name Haile Selassie, was crowned emperor. His reign was interrupted in 1936 when Italian Fascist forces invaded and occupied Ethiopia. The emperor was forced into exile in England despite his plea to the League of Nations for intervention. Five years later, British and Ethiopian forces defeated the Italians, and the emperor returned to the throne.

After a period of civil unrest, which began in February 1974, the aging Haile Selassie I was deposed on September 12, 1974, and a provisional administrative council of soldiers, known as the Derg ("committee") seized power from the emperor and installed a government, which was socialist in name and military in style. The Derg summarily executed 59 members of the royal family and ministers and generals of the emperor's government; Emperor Haile Selassie was strangled in the basement of his palace on August 22, 1975.

Lt. Col. Mengistu Haile Mariam assumed power as head of state and Derg chairman, after having his two predecessors killed. 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. From 1977 through early 1978 thousands of suspected enemies of the Derg were tortured and/or killed in a purge called the "red terror." Communism was officially adopted during the late 1970s and early 1980s with the promulgation of a Soviet-style constitution, Politburo, and the creation of the Workers' Party of Ethiopia (WPE).

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. In July 1977, sensing the disarray in Ethiopia, Somalia attacked across the Ogaden Desert in pursuit of its irredentist claims to the ethnic Somali areas of Ethiopia. Ethiopian forces were driven back deep inside their own frontier but, with the assistance of a massive Soviet airlift of arms and Cuban combat forces, they stemmed the attack. The major Somali regular units were forced out of the Ogaden in March 1978. Twenty years later, development in the Somali region of Ethiopia lagged.

The Derg's collapse was hastened by droughts and famine, as well as by insurrections, particularly in the northern regions of Tigray and Eritrea. In 1989, the Tigrayan People's Liberation Front (TPLF) merged with other ethnically based opposition movements to form the Ethiopian Peoples' Revolutionary Democratic Front (EPRDF). In May 1991, EPRDF forces advanced on Addis Ababa. Mengistu fled the country for asylum in Zimbabwe, where he still resides.

In July 1991, the EPRDF, the Oromo Liberation Front (OLF), and others established the Transitional Government of Ethiopia (TGE) which was comprised of an 87-member Council of Representatives and guided by a national charter that functioned as a transitional constitution. In June 1992 the OLF withdrew from the government; in March 1993, members of the Southern Ethiopia Peoples' Democratic Coalition left the government.

In May 1991, the Eritrean People's Liberation Front (EPLF), led by Isaias Afwerki, assumed control of Eritrea and established a provisional government. This provisional government independently administered Eritrea until April 23-25, 1993, when Eritreans voted overwhelmingly for independence in a UN-monitored free and fair referendum. Eritrea was with Ethiopiaís consent declared independent on April 27, and the United States recognized its independence on April 28, 1993.

In Ethiopia, President Meles Zenawi and members of the TGE pledged to oversee the formation of a multi-party democracy. The election for a 547-member constituent assembly was held in June 1994, and this assembly adopted the constitution of the Federal Democratic Republic of Ethiopia in December 1994. The elections for Ethiopia's first popularly chosen national parliament and regional legislatures were held in May and June 1995. Most opposition parties chose to boycott these elections, ensuring a landslide victory for the EPRDF. International and non-governmental observers concluded that opposition parties would have been able to participate had they chosen to do so. The Government of the Federal Democratic Republic of Ethiopia was installed in August 1995.