Any attack on Pakistan would have an element of surprise. US will certainly go for a preemptive nuclear strike so that Pakistan has little or no chance of retaliating against India and disturbing South Asian security.
Most probably, tactical nuclear missiles from USS Carl Vinson would capitulate Pakistan's war-fighting capability within a few minutes. Military and air bases with nuclear plants would be targeted and taken out.
And? What about the nukes? They're not located @ nuclear plants.
Most of pakistan's air force would be destroyed on ground. For the remaining: F-18s from Afghanistan
What about our ground assets & markers? By now, you should know that they can spot a fruit-fly coming our way. Afghanistan will be toasted in the mean-time. Don't counter this with OBL episode. Then you were not adversaries, now you're... You should know this after what happened to your special seal team *
and F 22s from UAE would establish complete air superiority over Pakistani airspace within a few hours.
As soon as we get a whiff, UAE and A-Rabs are the first targets of our "Strategic" assets.
Try explaining that to the millions of expats dead in those countries - how is that for strategic depth right in our backyard I bet you forgot this variable?
After that, India would naturally invade and take over Pakistan.
Never going to happen. India has a working parliament, long standing record of making the "right" decision; Contrary to majority of Pakistani "public" opinion they deserve more credit for their mature foresight. Conclusion: India will not be duped by double dealing US of A, and at the cost of "pin prick" that is Pakistan, get in bed with the vipers (US of A). So dream on!
US would not have to launch the ground invasion by itself and a ground invasion by US is unlikely. It would be very easy for India to take over Pakistan after the initial nuclear strike and air blitz by US.
* US troops are most welcome.
Even if they are armed with RPGs it does not matter. It just takes one nuclear bomb to kill 5 million people armed with nothing but rifles.