2. In 330 BC, Alexander the Great moved his armies east from Iran into northwest Afghanistan near present day Herat. After three years of terrible fighting, Alexander negotiated a shaky truce by marrying the daughter of an Afghan warlord who controlled large areas north of modern Kabul.
Alexander was thus able to declare victory and move his armies east toward India. The fighting in Afghanistan had been so difficult that Alexander was forced to leave behind nearly one fifth of his army - 10,000 infantry and 3500 cavalry - in order to discourage a rebirth of the insurgency. This sounds very familiar today.
The Afghan army was never an "army" by any modern understanding of the word. Rather, Afghan loyalties run to their own tribe, and, somewhat less so, to neighboring tribes. In the insurgency against Alexander, these tribes were aided in their ancient ability to merge the interests of these otherwise contentious neighboring tribes in order to face the common enemy.
More important, from the point of view of military tactics, Afghans moved quickly and silently over long distances and difficult terrain. They carried weapons, but very little food, or other battle gear. They fought dirty using their mastery of irregular tactics and weapons. Enemies of the Afghans also fought dirty, but with less effect.
The British army was defeated, and thrown out of Afghanistan in the 1840s. The Russian army was defeated and thrown out of Afghanistan in 1989. In our own war in that country today, it remains to be seen whether the US will learn the lessons of Alexander's war of over 2300 years ago.