One of the things (among others) that we in the west do not understand aboust the Middle East is the concept of blood feud. These feuds are very often generational, people there do not forget. This article on strategy page gives a good overview.
Deaths from revenge killings now exceed those from terrorist or anti-government activity. Al Qaeda is beaten, and running for cover. The Sunni Arab groups that financed thousands of attacks against the government and coalition groups, are now battling each other, al Qaeda, and Shia death squads. It's not civil war, for there are no battles or grand strategies at play. It's not ethnic cleansing, yet, although many Sunni Arabs are, and have, fled the country. What's happening here is payback. Outsiders tend to forget that, for over three decades, a brutal Sunni Arab dictatorship killed hundreds of thousands of Kurds and Shia Arabs. The surviving victims, and the families of those who did not survive, want revenge. They want payback. Read More.