I know it is pretty ignorant of me , but to me all Ethiopians =Habashi.
Indeed it's very ignorant to think so. Somalis hold the view that Ethiopia is Amhara and Amhara is Ethiopia.
This is usually because the Amhara have ruled Ethiopia for so long and the Ethiopian state (official religion, official language, etc.) have taken the identity of what has been labelled "Amhara culture" and the persons who have occupied power and privilege have by and large born from Amhara. The world education, and all till this day rely and take their sources from the Amhara which is why most people think Ethiopia = Amhara.
The rest of the ethnic groups who vastly outnumber Amhara in terms of population and territories were unheard to the world during the Amhara era, it was very recent that they came out in the 90s after the Amhara domination was put to an end but sadly, there was no effort to de-Amharize the country by the government today.
There are confused Somalis who have hard time distinguishing Ethiopia (a modern multi-ethnic nation) from Abyssinia (an ancient club exclusive to few in the Gondar region). Therefore we are obligated to teach them the difference and define the modern Ethiopia which is a federal and not so perfect democratic Republic.
So, let's be clear, more than 70% of modern Ethiopia and Ethiopians have no affiliation, association, connection or link with Abyssinia or the Amhara culture. Therefore it's wrong for the handful relics from the past to try to define Ethiopia as their private possession (Abyssinia).
Somalis may think Ethiopia = Habesha but to the Ethiopians (the home of 80 ethnic groups) and Eritreans (the home of 9 ethnic groups), Habesha refer to the major ethnic groups from the Highland region (Amhara, Tigray, Tigrinya and Guraghe).
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Back to the topic, Mengistu is from the south. In central and southern Ethiopia, if an Oromo is Orthodox Christian that individual may be classified as an Amhara regardless of his or her ethnic ancestry or lineage. He was never Oromo to the Oromos and most people in the Horns of Africa but was an Amharized Oromo who only served the interest of the Amharas.