Improving education, mental healthcare, reducing extremism, eradicating the constant divisiveness in everything, etc etc.
The overwhelming number of gun deaths that aren’t suicide are ordinary crime. Fixing the economic conditions that lead to crime would probably have the single biggest effect. Cramming tons of poor people into a small geographic area, and then ensuring that they have no realistic way out of poverty sure as shit hasn’t helped.
Extremism creates orgies of violence, but poverty creates the daily grind of violence.