Viewpoint: Why is Islamic State group so violent?

The filming of people being beheaded, drowned or burnt alive in Syria and Iraq; the bombing of a Russian passenger jet in Egypt; the mass killing of Christians in Libya and concert-goers in France: Why do Islamic State militants commit acts of such barbarism??

Charlie Winter, an expert in jihadist militancy, assesses the group's ideology, and suggests that grotesque acts of violence play into its wider strategy.

Video produced by Marcus Thompson