|First of all, I should mention that I am not advocating that kind of invasion at all. In fact, I think it would be a horribly bad idea. I am asking because someone on another forum suggested it and I would simply like to clear up whether the U.S. even has the capability to do it. I do not think United States of America does have the capability. Here is my response on that forum:
invading Pakistan would be an exceptionally bad move. First of all, Pakistan has nukes which it might well use to defend itself - although the U.S. would undoubtedly try to destroy them (as well as any nuclear facilities) with surprise air strikes in the initial stages of the war. Second, the U.S. would loose Pakistan's cooperation in the War on Terror thus enabling terrorists to regroup. Third, the U.S. does not have the capability to invade Pakistan. The U.S. military is already somewhat strained in Iraq (although troops are ready for another major theatre war in Korea...) so getting enough troops to invade and occupy Pakistan would be impossible. Even assuming the U.S. successfully took care of Pakistan's nukes and other WMD early on, Pakistani conventional military is vastly more powerful than the Iraqi one. On top of that, imagine the guerrilla war that would ensue... Pakistan has 150 million people the vast majority of whom are Sunni and hate the U.S. Compare that to Iraq's 25 million people of which only 20% (5 million) are Sunis that do the fighting. The word 'impossible' to occupy springs to mind... in fact, it would be impossible even if the U.S. did not have 25% of its army entangled in Iraq and did not have to stand by for another major theatre war.
In any case, how would even the invasion (not to mention the occupation) of Pakistan proceed? No neighbouring country except perhaps Afghanistan would allow the U.S. to station troops on its soil for the purposes of the invasion - not even India. The U.S. would have to airlift everything to Afghanistan - but how without being allowed to use surrounding airspace? No, an invasion from Afghanistan could at best be an auxiliary, diversionary thrust - the main force would have to come from the sea, as would the majority of aircraft. It would then have to move 2,000 kilometers north through Pakistan to get to Islamabad - the capital. On top of that, large parts of Pakistan are very difficult terrain for armour and mechanized infantry to move through... Again, the word 'impossible' manifests itself prominently in my mind.
Basically, the U.S. does not have the capability to even invade, not to mention occupy, Pakistan.