As far as being a staging area for a conflict with another country Afghanistan was always a bad proposition, due to the simple fact that for a staging area, one would expect to have good logistical access to it, while Afghanistan has the opposite of that. Geographically, the main way of getting troops and supplies to Afghanistan is landing them in Pakistan, an opportunistic frenemy country with not so great infrastructure, moving them few hundred miles through it, and then moving them around Afghanistan, a country with unfriendly terrain, unfriendly population, and terrible infrastructure.
All that to fight Iran? If you need an extra front to fight Iran that desperately, its not worth the effort to hold and supply such a vulnerable position, and if you don't need it, its also not worth it. For access to Iran, there's coast with nearby Gulf States who share the hostility to Iran, much more geographically convenient Iraq, and a NATO state of Turkey.
In the unlikely scenario Pakistan would turn out to be a loyal ally and support military operations, its own territory is probably more convenient than Afghanistan anyway.
China? The same massive logistical vulnerability applies, except more, due to China's influence in Pakistan and the border being on the other side of Afghanistan, and much harder battles ahead.
Basically, the only real purpose achieved by staying there so long was to make it harder for other state and non state actors to settle in, probably for one or two of trade routes, islamist friendly safe haven and mineral resources.
All that to fight Iran? If you need an extra front to fight Iran that desperately, its not worth the effort to hold and supply such a vulnerable position, and if you don't need it, its also not worth it. For access to Iran, there's coast with nearby Gulf States who share the hostility to Iran, much more geographically convenient Iraq, and a NATO state of Turkey.
In the unlikely scenario Pakistan would turn out to be a loyal ally and support military operations, its own territory is probably more convenient than Afghanistan anyway.
China? The same massive logistical vulnerability applies, except more, due to China's influence in Pakistan and the border being on the other side of Afghanistan, and much harder battles ahead.
Basically, the only real purpose achieved by staying there so long was to make it harder for other state and non state actors to settle in, probably for one or two of trade routes, islamist friendly safe haven and mineral resources.