In recent years we have begun to see some of Africa’s most notorious warlords being brought to trial – notably Charles Taylor and Thomas Lubanga. It now also appears that there is at least some chance one of the continent’s bloodiest tyrants – Mengistu Haile Mariam – will finally face justice. As Chairman of the Derg and later President of Ethiopia, Mengistu presided over what Human Rights Watch called “one of the most systematic uses of mass murder by a state ever witnessed in Africa” – the Red Terror of 1976-78, in which as many as half a million political…