Deep inside caves, in remote desert bases, in the escarpments and cliff faces of northern Mali, Islamic extremist fighters have been burrowing into the earth, erecting a formidable set of defenses to protect what has essentially become al-Qaida's new country. They have used the bulldozers, earth movers and Caterpillar machines left behind by fleeing construction crews to dig what residents and local officials describe as an elaborate network of tunnels, trenches, shafts and ramparts. In just one case, inside a cave large enough to drive trucks into, they have stored up to 100 drums of gasoline, guaranteeing their fuel supply...