Yemen: When Can We Call it "Civil War"?

Ovwr the past few days, Sana‘a' has dissolved into violent tribal conflict between the government and the forces of the Hashid tribal confederation led by Sadiq al-Ahmar; the Yemeni city of Ta'izz has been wracked by violence and multiple deaths after a ceasefire collapsed; and in the secessionist south radical Islamists have taken the town of Zinjibar.  (Semantically almost identical with Zanzibar, for sound historical reasons; remind me to write about that sometime.) The term "civil war" is being used more and more.

I'm unclear if there's some neat rubric that decides when, as a congeries of regional conflicts, tribal conflicts, and political violence coalesce, the conflict crosses the threshold into a "civil war," and I know some resist the term even for Libya (where it seems pretty well defined). Yemen is no stranger to civil war: the conflict of 1962-67 is universally so described, and so is the secessionist war of 1994. So when do we say the revolution in progress becomes a civil war? Yemen may be the poster child of the National Rifle Association: every male is armed with a sophisticated weapon (don't let the ubiquity and symbolism of the jambiyya [picture, right] fool you: the "full auto" selection on the selector switch on the AK-47 decides more political arguments).

Yemen has had so many regional and tribal conflicts that this new political conflict that is present throughout the country (though with different political aspirations and complaints in different regions)  leaves me unsure when exactly an endemic conflict erupting into a new metastasis is properly just an escalation, or needs to be categorized as a civil war.

I hope my Yemeni friends won't be offended if, given the country's history of regional and tribal dissent, the whole question of whether or not it's a civil war makes me think of the famous wit Dorothy Parker's alleged quip, when told that [proverbially boring and silent] former President Calvin Coolidge had died: "How could they tell?"