Apparently, it's not a civil war if the parties involved aren't religiously or ethnically distinct.
Among the most worrisome trends cited by the NIE was escalating warfare between rival Shiite militias in southern Iraq that has consumed the port city of Basra and resulted last month in the assassination of two southern provincial governors. According to a spokesman for the Baghdad headquarters of the Multi-National Force-Iraq (MNF-I), those attacks are not included in the military's statistics. "Given a lack of capability to accurately track Shiite-on-Shiite and Sunni-on-Sunni violence, except in certain instances," the spokesman said, "we do not track this data to any significant degree."
Attacks by U.S.-allied Sunni tribesmen -- recruited to battle Iraqis allied with al-Qaeda -- are also excluded from the U.S. military's calculation of violence levels.
This definition, of course, requires that we recategorize a fairly famous war of our own.