Qaddafi lost the tribes ...

"... This outbreak of clashes in the capital of Tripoli is important because governments are always most vulnerable in their own capitals, and because most of the 6 million Libyans live in the west of the country, where the capital is also located. Tripoli is a city of a little over a million. About 3 million Libyans, or half the country, live in the historic region of Tripolitania, including the capital and its environs. Populations along the North African coast hug the rainfall rich areas near the Mediterranean where agriculture is possible and there is potable water.
In a highly significant development, the leadership of the large and powerful Warfala tribe announced that it was now siding with the opposition against Qaddafi. About a million Libyans belong to this extended kinship group. Since cultivating tribal loyalties was one of the ways Qaddafi had remained in power, this major tribal defection underlines his loss of authority. It was further underlined when Arab Warfala leaders managed to convince their Berber counterparts in the southern Tuareg tribe, who are 500,000 strong, to join in opposing Qaddafi...."