Sunni and Shia

http://www.bbc.com/news/av/magazine-27945271/iraq-crisis-the-sunni-shia-divide-explained




https://www.economist.com/blogs/economist-explains/2013/05/economist-explains-19

https://www.nytimes.com/2016/01/04/world/middleeast/q-and-a-how-do-sunni-and-shia-islam-differ.html