An offensive by the armies of Chad and Nigeria deals blow to Boko Haram's "Caliphate" - but experts question whether gains will be sustained.
Boko Haram fighters have been driven from thousands of square miles of territory across northern Nigeria, dealing a significant blow to the Islamist movement’s ambition to carve out an African “Caliphate”.
As recently as January, Boko Haram controlled about 20,000 square miles of Borno and Yobe states, ruling a domain the size of Belgium with a population of at least 1.8 million.
Within this area, the Islamist
