Gun violence is closer to a pandemic than a war. Interestingly, we already know how to fix this (well some of it). Not just other nations, but various localities in the USA have tried the obvious things… and … they actually work. Death by suicide is the single biggest difference.
What to do, in approximate order (and the last one is the least important):
Require a cooling off period between “signing up to buy” a weapon and actually getting your hands on it.
Use that waiting period to actually look for red flags and priors.
Make red flag rules that actually work, actually require notification etc.
Limit the availability of particular weapons whose only reason for existence is to kill humans.