What does ISIS really want?

(CNN) – How to stop ISIS — it’s the question the leaders of the free world are struggling to answer.

The debate is frequently about tactics: How to gain a battlefield advantage, how to stop its propaganda machine, how to block its sources of revenue.

But less frequently is there discussion of the group’s aims — what it ultimately wants to achieve and the steps for reaching that goal.

The group’s rise in Iraq — and its capture of thousands of square miles of land — was so sudden and shocking that it left many analysts and officials flatfooted. A year ago, the New York Times published confidential comments about ISIS’ ideology by Major General Michael K. Nagata, then U.S. Special Operations commander in the Middle East.