ISIS is salafist... is some ways like their apocalyptic views they have more in common with hardline shia than with the average sunni.
The Sunni-Shia divide is overblown.
http://www.freerepublic.com/focus/f-news/2877454/posts
When the Ottoman empire dissolved, med like Churchill understood the Muslin mindset.
The creation of successor States to the Ottomans kept a lid on the Muslim Jihad