This is a long read but it should be required reading for anyone who seeks to understand ISIS and where they come from.
I don't agree with everything here, but it is eye opening. This is The Atlantic Mag.
It is not some conservative myopic. It is well done and very balanced. It gives some very interesting insights not only into ISIS but also into where mainstream islam meets radicalization.
There is also a very interesting section where a radical cleric explains what it is that islam is supposed to do. reading that gave me a very different understanding of why the American Progressives seem to be far less bothered by these guys than the American Right.
http://www.theatlantic.com/magazine/...-wants/384980/