Many of the details of the modernizations made before the fascist invasion during the Second Italo–Ethiopian War are written in Haile Selassie I's autobiography, My Life and Ethiopia's Progress Vol.
I (written 1938), particularly in Chapter 12, "About the improvement, by ordinance and proclamation, of internal administration, and about the efforts to allow foreign civilization to enter Ethiopia".
[1] Modernization was temporarily interrupted in 1935 following the invasion of Ethiopia by fascist Italy, eventually culminating in the Second World War.
As the Emperor himself noted in his Introduction to Volume I, "We were particularly convinced, by the policies directed against Us, that the enemy's heart was stricken with envy at Our setting up a constitution to strengthen and to consolidate Ethiopia's unity, at Our opening schools for boys and girls, at Our building hospitals in which Our people's health was to be safeguarded, as well as at all sorts of other initiatives of Ours by which Ethiopia's independence would be affirmed, not only in terms of history but in actual fact."
[5] He described in the whole of Chapter 14 his efforts to eradicate slavery, which he noted was a persistent custom in Ethiopia arising from intertribal wars, where the captured slaves could hardly be distinguished in appearance from their owners and sometimes even married them.