Afghans have a feudal sort of military organization. All the lads going off to war from a village, neighborhood or valley will follow the most charismatic and most battle experienced of their group. This guy will be the leader. Not an officer in our sense, but, well, the leader. Very democratic, but the leader might not know a lot about tactics or other military matters. These local groups, rarely more than a few dozen strong, will band together with similar size groups from their region under an even more famous and charismatic leader. This gets you a group of a few hundred fighters and an organization roughly comparable to what we call an infantry battalion. At this point, money becomes important. Whoever leads several of these battalions is usually wealthy, or is an exceptional battlefield commander who is backed by people with money. Someone has to pay for the food, trucks, ammunition and whatever else a popular commander can scrounge up (like medical supplies, artillery, tanks, helicopters, housing and even cash.) Several battalions gives what is called an "army" (we would call it an infantry brigade) and leader is often called a warlord by Western reporters.
The warlord's troops do not understand the concept of a Western army's discipline and ranks. In a Western army, any officer can order any soldier to do something. In an Afghan army, a soldier only obeys those leaders he knows. An Afghan warlord cannot be ordered to take part in an operation, but must be convinced via a war council. And even his assent does not always translate into consistent performance on the battlefield. Lacking the discipline of a Western army, an Afghan leader has to be very careful when it comes to casualties among his troops. This accounts for the unique way in which Afghans fight battles. Traditionally, Afghan warfare has been more about making an impressive show than getting right down to a hack fest and a lot of dead bodies. A warrior society won't last long if the warriors are too eager to get killed. These days, a loud and impressive display of firepower, but not a lot of casualties, best represents your typical Afghan battle. When someone does lose, and gets taken prisoner, they are often set free in a later exchange of prisoners. Afghan warfare can get very nasty. If the defender strongly resists, and inflicts a lot of casualties, the attacker will often massacre a lot of local civilians, especially if they belong to a different ethnic group.
The five year war between the Taliban and Northern Alliance has largely consisted of the more powerful Taliban trying to run the Northern Alliance troops out of Afghanistan (or getting them to switch sides.) Each Spring, the Taliban would begin gathering troops for a Summer offensive. A dozen or more Taliban brigades (often over 20,000 troops) would head north to clean out another Northern Alliance held region. Meanwhile, both the Taliban and Northern Alliance depended on local men-with-guns to hold the passes to their valleys or the high ground overlooking the roads the enemy trucks must travel to get to the local village. Most of the "troops" the Taliban and Northern Alliance claim are the men who stay home. But some of these guys do go off and join the "field army" for a few weeks or months. These are the lads in the trucks rolling off to attack, or help defend, some piece of real estate.
Real military power in Afghanistan comes from how many armed men you can put into trucks and move to other areas to attack or defend. Some artillery and a few tanks are also useful, but ammunition for these big guns is scarce, so the big stuff is largely for morale effect. Afghan campaigns are chess games, where each side shifts it's truck columns around to counter enemy moves.
Geography and climate has a lot to do with how battles are fought. Most of central Afghanistan is mountainous, with many fertile valleys. When there is only one pass into a valley, you can fortify that and hold off a larger force. When Winter comes, unsuccessful attackers usually have to go home. Trucks have a hard time bringing food to the troops when the snows start, and in the cold weather you also need heavier clothing and fuel to keep warm. Those defending their valley grow their own food, and can bring in small stuff like additional ammunition, over mountain trails. Why doesn't the attacker use those mountain trails to get into the valley? Because the locals know the trails better and can guard them with a few men.
Which brings us to another aspect of Afghan warfare; keeping the casualties down. An Afghan commander can see his troops leave for home real quick if too many of them get killed or injured in combat. Most Afghan battles result in very few casualties. When one side sees that it is outclassed and likely to be defeated, it just takes off in the night. If the defender is protecting their valley or town, they will start negotiating a surrender. Actually, surrender is too strong a word. The preferred move is to switch sides. This is why some areas are "Taliban territory" but not "Taliban controlled." The surrender options come down to becoming a Taliban ally (without Taliban troops occupying your area) or part of Taliban controlled Afghanistan (with the religious police and all the other stuff.)
When up against professional soldiers, the Afghans don't change their style. They will get their women and children out of the way, and then go after the soldiers. The Afghans won't attack unless they stand a good chance of success. They will flee from more powerful units. Instead they will attack supply trucks and smaller patrols. If you want to fight the Afghans and win, you have to find them first. But don't expect them to stand still and duke it out with a more powerful opponent. If professionals realize they are fighting warriors, and not regular soldiers, the Afghans can be beat. Otherwise, you are playing into the Afghan's strengths, and you will lose.
The Afghan Way of War- The Afghan's wage war in their own unique way, and it is quite different from what we normally think of as war. First, it is important to remember that Afghanistan is largely a warrior society, especially among the majority of the population living out in the countryside. An Afghan goes to war, not as a soldier, but as a warrior. As such, the Afghan warrior places more importance on honor and showing off than following orders and "accomplishing the mission." American troops carefully plan their operations and everyone follows their orders. Afghans will do what strikes their fancy and pay more attention to perceived slights than getting the job done.