Why Was ISIS Successful?

'Armies of Sand: The Past, Present, and Future of Arab Military Effectiveness' explains how the politics, economics, and culture of the modern Arab world has shaped the military power of the Arab states. Overwhelmingly, the impact has been negative, producing the vast tableaux of misfortune that has been Arab military history since 1945 and right up to the present day. It is why Arab armed forces have so consistently underperformed, losing most of their wars despite any number of favorable material factors.  It is also why their victories have been rare and typically modest, if not outright Pyrrhic. 
 
Yet in June 2014, ISIS—or Da'ish as it is referred to in Arabic—stunned the world by overrunning most of northern and western Iraq, seizing the massive city of Mosul, and causing five divisions of the Iraqi army to collapse. Much of its success was a product of the weakness of the Iraqi armed forces. However, some of it derived from Da'ish's own exceptional performance. Indeed, Da'ish and Hizballah are the two most important Arab non-state militaries that demonstrated a clear superiority in their battlefield competence over the vast majority of Arab militaries since the Second World War.  Understanding why they were exceptionally more successful is therefore a critical element in understanding how Arab society has shaped its armed forces during the modern era, and how the Middle Eastern military balance may change in the future.