I think the U.S. military, along with certain UN forces, would be used, and I think they would follow orders without blinking an eye.
I'm gonna have to disagree with this.
Having served a couple decades in the military myself, I can assure you that there are at least as many servicemembers, percentage-wise, who own personal firearms. They have no more desire, and probably even less, than the average civilian gun owner to give up their privately owned firearms.
To top that off, using federal troops against civilians is a HUGE move, and it's not going to happen outside of some kind of national emergency.
And even if it does...remember that our troops are volunteers, who come from all walks of civilian life. They are well aware of their roots. So to think that the troops will just "follow orders without blinking an eye" does a great disservice to them.
If we have troops who will speak out against, say, mandatory Anthrax vaccinations due to health and safety concerns, even to the point of ending their careers, don't think for a minute that we won't have troops speak out against a move to confiscate privately owned firearms.
What will more likely happen is a slow progression of ever increasing restrictions over a matter of decades. This is a war of attrition. Nip and tuck here and there until it becomes both not profitable for firearms companies to exist any more and people end up giving up their firearms for a variety of reasons.
When it becomes too difficult to comply with all the restrictions in order to participate fully in your gun hobbies, then your gun activities will die off.
When it becomes too expensive to engage in your gun hobbies the way you want to, then your gun activities will die off.
As you grow older and your children, grand children, and great grand children become progressivley less interested in firearms and related hobbies, their desire to own them will die off as well.
As society becomes more lenient to the ever increasing restrictions, every event that will allow it will see another change in the laws. More and more people will eventually make the decision that it becomes less worth it.
And if an armed rebellion happens? Well, now there is an obvious justification for the government to step in and stomp it flat. Everybody makes a big deal about why the 2nd Amendment is there. Take a good, hard look at the U.S. Constitution, Article I, Sections 8 and 9. And yes, the authority for the president to act is recognized by the Supreme Court.
Please give our troops the benefit of the doubt, here. They are as affected by these trying times as we are because of who and where they come from.