In 2014, the Islamic State shocked the world when it defeated national armies on the battlefield and seized large swaths of territory in Iraq and Syria. The group's military success can be traced to four key variables: organizational innovation, shaping operations, will to fight, and a knack for retaining the initiative. The IS military project led not only to the declaration of a "caliphate," but to the proliferation of jihadist franchises that devastated countries, displaced millions, and killed tens of thousands. Yet the group's weaknesses ultimately led to the collapse of its territorial achievement. Expert Ido Levy begins this pioneering study by surveying jihadist warfare from the 1970s to the present.

Sunni Jihadist armies before 2014 --Origins and elements of Islamic State military effectiveness -- IS performance in conventional operations -- Sources of IS military effectiveness -- IS military operations outside Iraq and Syria -- Assessing the Islamic State's way of war -- Lessons learned and policy implications.