What would be the point in going to Pakistan? There's no oil there only thing Pakistan has that's of interest to the "west" is terrorists by the looks of things.
Faisal were you born in Britain? Or have you migrated here? of you don't mind me asking of course, just out of interest!
Open the world's map and have a look at the Pakistan's map! They're next to the IRAN!
THe USA wants to get the OIL from IRAN - they want to OWN their oil and make billions on it to do that they need a place to attack - obviosly from the Sea with their fleet but it makes the job harder to attack from the sea only, so they need a piece of land to make a base for their troops - therefore Pakistan would be ideal as it's next to the sea and they can deliver all the troops and vehicles by the sea!
As they already own the IRAQ they can attack Iran from both sides then from the Iraq and Pakistan and they already have some troops in Afghanistan + the Sea! If you do some research Iran's army is pretty big (well compared to Iraq let's say), so they will need more troops/vehicles to conquer it and ideally to attack from as many sides as possible - this way Iran won't be able to concentrate their army at one spot.
To do that they will need a reason - I won't be surprised if we'll have another 911 soon and that would be a "reason" to attack the Iran!