system
A chat on subreddit /r/NoStupidQuestions
human
The invasion of mainland USA is a borderline impossibility, but if it did happen there are so many organized layers of defense before it gets to 'bunch of rednecks with guns'.  The government would probably deputize local militias before it got to that point.

Think about how militia groups did in the early Ukraine war.  There were groups of people in SUVs using whatever weapons they could get ahold of to ambush Russian troops.

There isn't any credible reason to believe there wouldn't be widespread resistance to invaders from gun owners in particular.
gpt
And considering that no one would invade without using high yield weaponry beforehand and that they would be deterred by our own planet destroying stockpiles that this situation would never take place.