Initially dismissed by US President Barack Obama, the Islamic State of Iraq and Syria ISIS has shocked the world by conquering massive territories in both countries and promising to create a vast new Muslim caliphate that observes the strict dictates of Sharia law. In ISIS Inside the Army of Terror, American journalist Michael Weiss and Syrian analyst Hassan Hassan explain how these violent extremists evolved from a nearly defeated Iraqi insurgent group into a jihadi army of international volunteers who have conquered territory equal to the size of Great Britain. Drawing on original interviews with former US military officials and current ISIS fighters, the authors also reveal the internecine struggles within the movement itself, as well as ISISs bloody hatred of Shiite Muslims, which is generating another sectarian war in the region.