The newly announced U.S. strategy of chasing away the Taliban, thus allowing Afghan forces to move in and provide sufficient security to keep the Taliban from returning (from either mountain hideouts, or, more likely, bases in Pakistan), depends on several things that have never occurred before in Afghanistan. First, there's never been a "hands on" central government in Afghanistan. Instead, the nominal ruler in Kabul dealt with foreigners and moderated some of the disputes between tribes (more common in the south) and warlords (more common in the north). Effective central government is difficult to achieve, as the history of the world during the last few centuries amply demonstrates. Many of the nearly 200 nations on the planet, like Afghanistan, have a central government in name only. Some, like Somalia, don't even have that. It's feared that, if the American plan doesn't work, we'll have another Somalia. Well, at least there won't be a piracy problem.
The fighting has already begun, with American and NATO forces engaged in several dozen operations. These battles concentrate on Taliban and al Qaeda bomb (roadside and suicide) operations. Al Qaeda still exists in Afghanistan, but tends to be integrated with Taliban groups. The Taliban is actually a federation, with dozens of separate organizations, each led by an experienced and ambitious guy, some of whom may be immune from getting fired (because of powerful patrons).
What really drives the Taliban is money (from foreign donors, local crime and for providing muscle for drug gangs). U.S. and NATO operations tend to go after any al Qaeda activity they detect, but have far more targets when they look around for Taliban fund raising. The money is important because, while Afghans will act on personal or tribal beliefs, what really motivates people here, in the poorest nation in Eurasia, is money. Afghans live on the edge of survival, and the money is often a matter of life and death. Moreover, there's not much of an economy, and not many jobs, out in the countryside. But there are lots of guns, and the Taliban is there to hire the guns so they can put the Pushtuns back in charge of the country. Right now, the non-Pushtun majority (mainly the ethnically similar Tajiks) have the most power in the central government, the army, and northern Afghanistan.
That raises another issue. If the foreign troops leave, and the central government is not strong enough to contain the Taliban movement, these Pushtun religious fanatics will again, as they did in the mid 1990s, take control of southern Afghanistan (and Kabul), and there will commence another civil war (like the one that was still going on when the U.S. invaded, with a few hundred Special Forces troops, and several thousand smart bombs, in October, 2001.) The Taliban, then as now, will use the tax on heroin production to keep their government going, and al Qaeda will again have a safe haven (OK, not as safe as before, but a sanctuary of sorts). Pakistan will probably have crushed the Taliban on their side of the border, just as they chased out the heroin production business in the 1990s. Pakistan will, then as now, make deals with the Afghan Taliban, in order to keep the peace on the border area.
Meanwhile, the drug gangs are having a bad year. U.S. and NATO forces have been all over Helmand province (where most of the world's heroin is produced). The Taliban have also suffered, because they also use Helmand as a base (as this area, and nearby Kandahar city, are the Taliban homeland). The additional U.S. forces are meant to cripple Taliban power in their Helmand/Kandahar homeland. Key battles in this war are going on right now, and most of the 30,000 American reinforcements will join this fight.
Without their Taliban muscle, the drug gangs have a Plan B. That involves using all the government officials (provincial and national) they have on the payroll, plus the non-Taliban gunmen (thousands of them) the gangs maintain for security, to provide protection from the foreign troops. The drug gangs can be hurt so bad that they will move to another country (that's what happened in Pakistan two decades ago, and in other parts of the world as well). But many Afghans will lose their newfound fortunes if that happens. In a country as poor as Afghanistan, men will fight hard to retain the wealth they never thought they would possess. Expect to see some interesting moves in Kabul, as the drug lords pull strings to get their guys to somehow call off the foreign dogs.
December 1, 2009: The U.S. has finally announced its new Afghan strategy. An additional 30,000 troops are going to Afghanistan, during the next six months. But the plan is for all, or nearly all, U.S. troops to be out of Afghanistan in 2-4 years. The U.S. has asked its NATO allies for an additional 10,000 troops, but was told that 5-7,000 was more likely to actually arrive. With over 150,000 foreign troops, NATO believes it can clear the Taliban out of areas (in the south) they have long used as bases, and allow the 150,000 Afghan security forces to establish control. Then the foreign troops can leave. That's the plan.