The British, after librating Ethiopia from Italian rule in 1941, occupied Ethiopia themselves. It would take more than a decade before Britain was to completely surrender all land belonging to Ethiopia. The British military took position of Ogaden and other areas near Djibouti. The British dictated to the emperor how to conduct all matters of governorship and nothing was to be put forth without their approval. The emperor at first did not have much of a choice for he feared further retaliation from the British. It would take until the end of 1944, after much diplomatic bargaining, that the British started to relinquish power to the emperor. They returned Ogaden in 1948 and returned all other areas belonging to Ethiopia by 1954 (Pankhurst, R. 251-6). Eritrea, which had been an Italian colony since the 19th century, became part of Ethiopia upon the decision of the UN General Assembly (Pankhurst, R. 260-1).
During 1940s and the 1950s, Ethiopia was rebuilt. The US became an important partner in the reconstruction. The Americans helped Ethiopia set up an airline, reestablish money currency, fund the building of roads, and train the army. Besides the US, Ethiopia was assisted by the British, Swedes, Germans, Israelis, Yugoslavs, Indians and other African nations (Pankhurst, R. 256-9). This period also so the emergence of Ethiopia as a leading African nation. As many other African nations began to gain their independence in the 1950s and the 1960s, Ethiopian diplomats and leaders began to get involved in African politics. This led to in 1963 to Addis Ababa becoming the seat of the OAU (Organizations of African Unity) (Pankhurst, R. 263-4).
All was not well in Ethiopia during this time, however. Many were unhappy with the slow economic growth Ethiopia was experiencing. Many wanted land reform but the landowner dominated legislators of government were fine with just they way things were. Many felt the monarchy was a system of government that was outdated. In 1960, the Imperial Bodyguard, while the emperor was away on a foreign trip, attempted a failed coup. During the 1960s, the intensity of the student body protest increased year by year. The infamous famine of Tigray and Wallo in the 1970s led to the rise in cost of food. Oil prices spiked in 1974. These events led to massive protests and strikes (Pankhurst, R. 265-6).
During the unrest, a group of radical members of the armed forces slowly began to acquire power. They began to detain members of the monarchy. They took control of the media and started to spread damaging propaganda against the emperor. On September 12, 1974 they arrested Haile Selassie, ending his rule and the monarchy.
Pankurst, Richard. The Ethiopians. Oxford: Blackwell, 1998.