A couple of days ago someone asked me a mainstream question: "when will the war between Sunnis and Shiite end?" Briefly, — Some Alawite (Shi'a) generals and officers defected from the Syrian army at the beggining of the uprising and joined the Free Syrian Army. — The Sunni bourgeoisie in Damascus is not fightng Assad. — The main force which has been fighting ISIS on the ground is a Kurdish one. The Kurds are Sunnis and ISIS fighters are Sunnis, too. — Many Syrian Sunnis who have been displaced because of the war have fled to "Shiite" areas. They haven't been killing each other. — The rest is geopolitics. Example: The Northern Alliance in Afghanista, although it included some Shiites, was mainly led by a Sunni-Tajik, Ahmed Shah Masoud. The Aliance was supported by Iran, among others such as Pakistan and the US. Masoud was assassinated by Taliban, a Sunni organisation.
“The West won the world not by the superiority of its ideas or values or religion (to which few members of other civilizations were converted) but rather by its superiority in applying organized violence. Westerners often forget this fact; non-Westerners never do.” —Samuel P. Huntington, The Clash of Civilisation and the Remaking of the World Order, 1996, p. 51