“When I interviewed ICSR director Peter Neumann in September 2015, he explained that there were four main reasons he'd found for why ISIS fighters quit:

1. Recruits joined to fight Bashar al-Assad, but ended up largely fighting other Syrian rebels, and were disappointed by this.

2. Defectors believed ISIS was too brutal to fellow Sunni Muslims.

3. Defectors said ISIS leaders were corrupt and played favorites.

4. Many also said living conditions in ISIS territory were awful; they'd been promised a glorious caliphate but found squalor.”