We started on this one a couple of weeks ago, a few days after ISIS took Mosul, and it became clear that this was going to become an ongoing story.

The main way we (in Graphics) have been trying to keep up with the crisis is through this frequently updated stack of maps and charts:

http://www.nytimes.com/interactive/2014/06/12/world/middleea...

... so, this piece is intended to contrast with the stack, and be a bit larger in scope, a bit less news-item-y, and a bit of a deeper dive into the rich background of the situation.