Hey there, sorry for the delay in answering this question.

First off, there is a Horn of Africa section of the book list which mentions several books. of course, only the Hatke book and Phillipson's Foundations of an African Civilization focus specifically on Aksum/Ethiopia.

Saheed Adejumobi wrote The History of Ethiopia which is much more focused on modern history, and particularly strong in explaining the 20th century.

Harold Marcus wrote A History of Ethiopia which is a good introductory overview.

There's also Stuart Munro-Hay's Aksum; an African Civilization of LateAntiquity available as a pdf here.

Richard Pankhurst has written a great deal about the history of Ethiopia, though his work is older.

Tadesse Tamrat was an eminent scholar who wrote Church and State in Ethiopia which is still essential reading regarding the ethiopian church and the monarchy.