The countries have disagreed about their border since Eritrea gained independence from Ethiopia in 1993, but remained staunch allies, anyway. One reason is historical. Eritrean rebels played a pivotal role in the alliance of Ethiopian rebel groups that ousted the Marxist dictator of Ethiopia, Mengistu Haile Mariam, in May 1991 and set up the current government. Details of what occurred are sketchy. Ethiopia says Eritrean troops crossed into its territory, ransacked health centers and schools and kidnapped civil servants.
Ethiopian officials maintain that the troops are still inside their territory.