When the British teenager Shamima Begum ran away from East London to join IS, the caliphate was at the peak of its powers. It waged war with the West by beheading hostages and carrying out deadly attacks on European soil, while establishing a sophisticated state infrastructure in Syria and Iraq. IS at one point controlled an area the size of Britain. But now, as Shamima Begum waits in a Syrian refugee camp to see if she’ll be allowed home, IS is on the brink of military defeat. Does that mean that the threat is over? In the first of two special episodes, the BBC’s Quentin Sommerville takes us through the rise and fall of IS.

Producers: Harriet Noble and Duncan Barber