In 1960, two brothers were nearly successful in deposing the emperor. The leading figure in the failed coup was Garmame Neway, who was educated in America and had become very dissatisfied with the backwardness of Ethiopia. Garmame's brother, Mengistu, was in charge of the Imperial Bodyguard. With the aide of his brother and other conspirators, the coup was launched on December 14, 1960. That day, the emperor was away on a foreign trip. The rebels rounded up prominent politicians and held them hostage. They took control of Addis Ababa and announced that the monarchy had ended and that a new government had been created. Students demonstrated in the streets to show their support. (Zewde, B. 2007, 211-5)
Not everybody was ready to depose the emperor, however. The army and the air force chose to remain loyal to the emperor. On December 16, fighting broke out and the rebellion was easily crushed. The brothers killed some of the hostages and fled. Germame was killed in fighting and Mengistu was prosecuted and executed. (Zewde, B. 2007, 211-5)
Zewde, Bahru. A history of modern Ethiopia 1855 1991. 2nd ed. Addis Ababa: Addis Ababa University Press, 2007.