They don't credit him cause Africa is home to dictators and tyrants who kill their own ppl.
the AU have given tribute to many african leaders like kwame Nkrumah jomo kenyatta etc and even haile selassie, but i never hear them speak of aden cadde. infact aden cadde and kwame became president of their countries on the same day.
aden cadde has a unique history compared to the other many leaders of africa, his regime was never toppled, he was a foundin member of the AU in '63, he went through two presidential elections and a national war, all without upheaval. to top it off, he lived in his farm in his own country throughout the rest of his life and his life was never in a major political threat, even during the height of the civil war. and he recieved a state burial when he died. if the AU gave credit to anyone, it should have been him.
