Define "civil war"

Andrew Sullivan has posted an email from Iraq:

Today I witnessed - from a safe distance - my first car-bomb. Then went back to read reports of 13 judicially sanctioned executions, 32 extrajudicial killings discovered, 50 bodyguards taken hostage ... Westerners talk about their hotels not in terms of spa amenities and availability of Starbucks, but based on the number of blast walls between the building and the street. So imagine where on earth people would think the arrival of a massive sandstorm was a blessing. I was amused to see Condi and Rumsfeld on TV - carried live on a local TV feed. I watched it in a crowded lobby. I'll just say the reaction of those around me was derisive - no difference in that between the locals and the Americans, all of whom (except me and the journos) seem to be DOD contractors. Possibly they're even right about the use of the term "civil war." If that evokes memories of Spain in the 30's or America in the 1860's it would be misleading. What's going on here is something very different from that. It's more a communal disintegration.

Over the weekend, I invite everyone to post comments on how they think a civil war should be defined. Please do not try and preclude Iraq from any declaration (either affirmative or negative) based on your definition. I'd like to see an honest and thorough debate about the definition of civil war. If you have links and sources, that would be excellent.

It seems that in the coming weeks, and I fear months, the definition of civil war will be at issue. Thanks.