As much as I think any war with Iran is about protecting Israel, I can see that the goal would instead turn to regime change. This is the #1 reason that Iran will build nuclear weapons, and that is to prevent invasion and toppling of their government.
If Israel triggers the toppling of the Islamic republic, the US and their allies will be dragged into it and the ramifications are huge. I highly doubt Israel would be nuked, but with NATO forced on Iran, there will be alliances made to free Iran (which holds holy places for Shia Islam).
If American doesn't make peace with the Taliban, the Taliban will find new allies among Shia groups like the Shia Hezbe Wahdat that have now been friendly with the US in Afghanistan. There will be hordes of Shia's from the tribal lands between Afghanistan and Pakistan that have been friendly with the US, turning their backs. You will see Shia's from India, Pakistan, Afghanistan, Iraq, Bahrain, maybe even China, getting armed and ready to attack US interests throughout the region. Their goal would be to free Shia Islam's holiest cities from Western forces creating new Bin Ladens of the Shia Design.
With the alliance of Sunni and Shia armed groups, there will be regional instability in Iraq, Afghanistan, Pakistan, Shia regions of the Middle East and I doubt the US will be able to contain them all. It will be death by a thousand cuts for NATO.