Pssssst! We ain't leaving A'stan. We're making it look like we're leaving but the reality is too much at stake to go away.
-- A'stan is the keystone of the encirclement strategy afoot for containing Russia.
-- It serves as a blocking location to stop the westward movement of China's influence.
-- The country is a Disneyland of undeveloped mineral resources, a lot of which are rare earth minerals.
-- So far no oil deposits worth mentioning but that could change with the involvement of Russian technology and smarts (see previous comments).
-- It serves as an outlet to the sea for oil produced in the Stans (aka southern Russia).
-- A'stan has a lock on world heroin production. The US could have shut down heroin production at any time over the last 10 or so years yet failed to do so. There exists an increasingly influential body of thought which maintains the only real international currency is raw opium, something international banks maintain an interest in.
-- Oh, A'stan sits on the eastern border of Iran, the Bad Guy of the Day.
No, we're not leaving. Instead we are burrowing in like a tick. Did we fail in A'stan? No, looks like we've been quite successful considering the commercial consequences of sticking around.
c.f. any book by Z'Big or Google up "silk road strategy"
