I see a number of political blogs saying that Afghanistan is impossible to conquer, or impervious to outside control; and they cite the British, the Russians, and (in the better-read cases) Alexander. I think they are making a mistake. Just for starters, they are cherry-picking the data; what about those tribes from the southern part who did manage to hold the place together as a moderately coherent kingdom? Just being from Afghanistan isn’t magic pixie dust that makes the mountains go away, or cause the other tribes to like you any better. Rather the opposite! And similarly for the Taliban, who were doing a pretty good job of ruling the place to their tastes until they ran foul of the invasion; it’s not as though they were a dearly loved regime.
Then, consider that the British campaigns were fought with literal muzzle-loading, black-powder rifles (the British ones not substantially better than the Afghan), with logistics tails limited to horses and camels, and backed by a military-industrial base that was either nonexistent (India) or three months’ sail distant (Britain) and minuscule by modern standards. Although Afghanistan is no poster child for infrastructure, there certainly has been some improvement since 1851! And besides that, just how many of the lessons of a pre-mechanisation army (pre-railroad, even!) can you really apply to one with trucks, aircraft, and satellites? It was always logistics that was the limiting factor; I think it’s safe to say that the imperial powers’ logistic ability has improved rather more than the fighting power of the tribes. The AK-47 is not as large an improvement on the jezail as a truck convoy is on camels.
What of the Russians? They weren’t doing so badly as all that, holding the place down; certainly they controlled the main valley corridor. Which, while it doesn’t look so impressive on a map, contains most of the population and most of the productive capacity, such as it is. The Americans didn’t supply the Taliban with SAM missiles out of the simple goodness of their hearts; they were worried that the Soviets were winning. And this was in the 80s, with the Soviet economy moribund to the point of near collapse and the empire fraying at the seams.
It’s also worth keeping in mind that these same predictions were made back in 2001; “Afghanistan is unconquerable”, it was said. And then the Taliban’s armies in the field collapsed under a hail of precision bombs, and the campaign ended in three months. There’s nothing magic about mountains.