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The group built quickly, claiming space left behind by the Syrian civil war and the chaos in the wake of the long US war in Iraq. By mid-2014, the group known to many countries as "Daesh" had declared a caliphate. Within a year it had claimed larges swathes of land in Iraq and Syria, gained affiliates and inspired followers in more than a dozen other countries -- and begun a reign of terror for any who did not conform to its rigid, violent interpretation of Sharia law.

In late 2015, the self-titled Islamic State, aka ISIS, became the focus of international military action that included airstrikes, weapons deliveries and eventually, bloody, costly door-to-door combat in Iraq and Syria. The manhunt was on for affiliates in other countries.

In Shatter the Nations: ISIS and the War for the Caliphate, Mike Giglio tells the story of the rise of the caliphate and "the ramshackle coalition -- aided by secretive Western troops and American airstrikes -- that was assembled to break it down village by village, district by district." Giglio spoke to Stratfor's Fred Burton for the Pen and Sword podcast.