I just want to add
It takes Months and months to build up a invasion force
Then you have to have a safe area to build that force up in
You then have to decide how you are bringing troops across, by air, which will take a long long time, or by ship in which case you have to slowly go through the Hormuz
And that doesn't include all the equipment, arms, food and everything else that is needed
And on top of all the above, you have to hope that Iran doesn't bomb the shit out of you whilst your putting together that force
Boots on th ground is not viable
Now special forces, sure maybe
Terrorists or Kurds etc, again possible
Internal riots/protesters, again possible
Iran will have to be ready, but a invasion is out of the question, but Iran should look out for protesters and terrorists and special forces