A quick review. In 2001, the US, with international support, invades Afghanistan. Support from Pakistan is critical in this matter, as the map makes clear - US forces came to Afghanistan primarily through Pakistan and Uzbekistan. As Afghanistan was in a state of civil unrest, it was fairly easy for US forces to depose the Taleban.
Use of Pakistani airspace was necessary, but entirely usable. The US installs a permanent military presence in Afghanistan. The new Afghanistani government has no choice but to accept it.
2002: Bush describes "Iraq, Iran, and North Korea" as an "Axis of Evil."
2003: The US invades Iraq, allegedly in order to control . Support from Turkey, whose interest is in there
not being a Kurdish state established, is easily obtained and highly useful. The demoralized Iraqi military - whose existence was primarily to fight against Iran - collapses easily.
The new Iraqi government has no choice but to accept an apparently permanent US military presence, although
mounting protests suggest that the US will have to start drawing down troop presences.
The US makes noises about Syria having received Iraq's WMD, but this drumbeat is dropped after a while.
Now, North Korea is in no real danger of being invaded - nor, for that matter, are we ready to try and conquer Pakistan or Turkey, although the propaganda machines make it clear we are supposed to be uncomfortable with Pakistan. Both may or may not allow us to use their airspace or station troops through their borders; both have very strong militaries.
However, firm control of Afghanistan and Iraq puts us in a perfect position to invade Iran,
with or without help from any of our Islamic allies. Our air bases in Saudi Arabia can be used for airstrikes; such could also be performed from the Indian Ocean. We can engage Iran from
both directions.
This seems likely to succeed. The only surprise is that this hasn't started yet. I suspect the administration does not trust success to last against Iran (a far more stubborn and unified opponent than Iraq or Afghanistan), and allowing only the initial phases before the midterm elections will have the population at its best achievable war-fervor.
Conquering Iran also allows installation of military bases there. A US military presence in Iran allows supply of operations in Afghanistan and Iraq that
doesn't pass through independent Islamic nations, particularly Pakistan - allowing the administration to harden its stance towards Pakistan, or - should future administrations be even more in favor of war on the entire Islamic world - start in on Syria and Jordan with minimal justification the next time they have a spat with Israel. After all, there would be an occupied US imperial presence right there.
At this point, I doubt that any invasion of Pakistan is planned for the immediat future, due to Pakistan's ability to reach Israel with the nuclear weapons it has stationed on the Iranian border; however, you can bet that the moment Pakistan starts to experience serious political upheaval, US forces will be there to "stabilize" the situation in their favor.