I'm not sure if it's still a thing, (if it's not, I'm sure that some of my friends on the left will fact check me for free), but I seem to recall reading that in Israel not only is it mandatory to serve in the military, but you're carrying your service weapon 24/7 while you're in and you keep it when you seperate from active duty. I THINK that Sweden (or Switzerland) has a similar set up, all adults must at least own a firearm.
Another nice tale that will probably get shot full of holes (pun intended) is that Admiral Yamamoto was never in favor of invading the U.S. mainland because he said something to the effect that there would be a gun behind every blade of grass.
Then there was that time that Russia and Cuba did invade the U.S. and some kids in Colorado formed the resistance...oh, wait, nevermind...
Point is, an armed populace is not only a deterrent to all enemies, foreign and domestic.