The sparse population is easily maintained by their scant domestic production. They get supplies from the south and Pakistan, from the west and Iran, and from the north and the central Asian republics, many of which have their own armed resistence groups in the field. They pay for imports with aid from Pakistan - which can indeed be cut - and by growing poppies, processed into heroin. Also some exports of handcrafts like rugs.
When the Russians fought them, they drove a quarter of the population over the borders to Pakistan and Iran, into refugee camps. They killed or wounded another quarter of the population, including carpeting bombing mere villages, large scale use of heavy armor and artillery, plus literally millions of land mines, many of which are still there. So are the Afghans.
Ref your #38: Good post and info. BTW, thousands of Afghan refugees are now expected in Pakistan (some already arriving).