Author JM Berger. Photo: Janet Walsh.
JM Berger has co-authored a book on terrorism ISIS - The State of Terror, with Harvard lecturer Jessica Stern, looking at the dramatic rise of Islamic State.
The brutality of the radical Islamist group has sent shock waves around the world – mass killings, abductions of religious and ethnic minorities and the beheading of soldiers and journalists – the like of which hasn't been seen in recent times.
JM Berger is an analyst and consultant on extremism; he is also the author of critically-acclaimed book Jihad Joe - Americans who go to war in the name of Islam.