Eritrean–Ethiopian War
Eritrea's war of independence lasted for 30 years, on and off; it was started in 1961 and finished in 1991 when Eritrea finally became independent.  While this was going on, there was also a civil war in Ethiopia, which began in 1975.  This war was started by Tigray People's Liberation Front (TPLF) as a rebellion to overthrow the Marxist military dictatorship of Derg (a military committee that had overthrown Emperor Haile Selassie in 1974).  TPLF and the Eritrean People's Liberation Front were formidable allies during the civil war, but then Ethiopia and Eritrea could not agree on where the border was after Eritrea's independence.  One of the main areas of conflict was focused on Badme.