I want to know the answer to the following question:
When did Eritrea join a federation with Ethiopia, the Federation of Ethipia and Eritrea?
All the background I'm provided with is that "Hostilities between Eritrea and Ethiopia persisted, leading to the Eritrean–Ethiopian War of 1998–2000 and further skirmishes with both Djibouti and Ethiopia.". Is that enough to answer the question?