It's a consequence of the puritanical roots of US. It's a fetish for punishment.
I never understood the "fetish" of Hollywood for the lone ranger and bullet slinging revenge guy. Or the idea that guns are a valid protection.
Non the less - there are other parts of the world that maybe have the same (or even higher) amounts of guns in private possession without the military and police fetish.
I am even not sure, that this is a valid correlation. Private gun ownership and police/military spending/fetish.
Wikipedia seems to back up my first thought: https://en.wikipedia.org/wiki/Estimated_number_of_guns_per_c...