It appears that Yemen has crossed that threshold from political crisis to civil war. From The Christian Science Monitor:
After months of trying to tamp down unrest, Yemen’s embattled President Ali Abdullah Saleh and his security forces have become embroiled in a conflict that meets all the classic definitions of a civil war.
He and his security forces are now fighting on three main fronts: In the capital of Sanaa, Saleh loyalists are engaged in a pitched battle with tribesmen under the direction of Sheikh Sadiq al-Ahmar, leader of the powerful Hashid tribal confederation; Islamist militants have taken control of the southern province of Abyan; and in the southern city of Taiz, Saleh’s Republican Guard violently dispersed protesters. Yemeni government forces have reportedly killed more than 50 people since Sunday.
I fear Yemen is sliding down a path of tribal based militias, none of which are strong enough to maintain control — but just powerful enough to prevent their rivals from asserting dominance. That path may very well lead to a Somalia-like situation of competing militias, foreign interference, religious radicalism and — above all — a dismal future for civilians caught in the conflict.
At the rate it is going, if you want to peer into the future of Yemen, just glance across the Gulf of Aden.