I concur with Godfather, how long do you intend the US and the UK to be there for? Till the end of time? Pakistan live RIGHT NEXT DOOR to India, who also have a nuclear armament and despite the fact that neither country particularly likes each other, they have resisted the urge of nuclear armageddon, which you are implying will happen to a Western country if we leave Afghanistan.
Prehaps Russia and China should invade Canada or Mexico to keep an eye on the USA??