The Eritrean War for Independence was a bloody 30-year war fought between Eritrean separatists and Ethiopia (under various administrations) from 1961 to 1991. I understand that the conflict was triggered by Ethiopia annexing Eritrea (they had been joined in federation per UN decree since 1952), but I still don't understand the root of Eritrean discontent with Ethiopian rule. What Ethiopian policies or actions motivated the Eritrean separatists to begin their armed struggle?
Eritrea had been a separate state for a long time and has a distant proud history. Ethiopia could not have forced federation upon Eritrea without the intervention of the UN (principally USA and GB). Eritrea was not consulted.
"In 1962 Ethiopia formally annexed Eritrea, dissolved the Eritrean Assembly and placed the country under what was effectively military rule." Again Eritrea were not given a chance to argue their case.
I took the quote and this information mostly from "The Bradt Travel Guide to Ethiopia", pages 33 onwards, by Philip Briggs, 3rd edition published 2002 and suggest this could be a good starting point.
I have been reading newspaper reports on this subject, just out of interest, for about thirty years so you could try some newspaper archives next.