I'm saying the Czech Republic has shall-issue concealed carry, and shooting in self-defense there is legal (as long as alcohol isn't involved iirc and other exceptions like that). Despite that, they have a very low homicide rate (one of the lowest in Europe). Maybe we should look first at where gun violence is worst in the United States, that being among black males aged 16-24 who commit and are victimized by roughly half of the entire nation's gun violence. Legalize and regulate drugs broadly like Portugal did, remove a lot of financial incentive behind gangs in America as well as part of the reason single-motherhood is so much more prevalent in those communities. Overhaul the worst schools, have a constant police presence if necessary, removing violent students immediately.
Take care of that, then maybe look at alcohol abuse and domestic violence next. Drunk idiots killing each other at or outside of bars is another common reason behind gun violence in the USA. I wouldn't necessarily be opposed to blood alcohol limits for firearm operation (although I'd personally rather see much more strict punishment for people that show violent behavior while intoxicated in general).
I think the prostitution point mentioned that momeNt brought up could be a valid one too. Men do crazy shit when they're horny, and off the top of my head I remember reading that during a time when Rhode Island had legal prostitution via a loophole, their rate of rape actually decreased by quite a bit. I'm not sure how well that translates over when it comes to gun violence against women, but I also know that lack of sex is a risk factor for suicide among men, at least, and certainly there have been a few notorious spree killings spurred by desperate sexless men (noting of course that spree killings are a small and insignificant portion of total gun violence).