The Taliban and al Qaeda have joined forces with tribes involved in the drug trade. Together, they are opposing and corrupting the government (which isn't very strong to begin with.) The drug gangs can only exercise some control over some parts of the country some of the time. The government troops can always come in with some American Special Forces troops, and US heavy bombers overhead, and do what they want. But the country is large and the government forces can only cover a small portion at any one time. The drug gangs prefer payoffs to gun battles, although the gangs can afford the latest in weapons and other gadgets. The fighting in the south is nothing new, it's been going on for centuries as kings or foreign conquerors tried to exercise more control than the tribes were willing to tolerate.