And yet so many other developed countries are significantly less violent than the US, despite having far fewer guns in the hands of civilians

I wonder what things they have in common, if guns don’t seem to be a factor.

Maybe we could figure out whatever that is and work on that, instead of focusing on gun ownership, which demonstrably does not lead to more violence, and in most cases, leads to less violence.

Those countries tend to already have better economic safety nets / welfare systems and mental health systems, thus mitigating the reasons why someone might be driven to engage in violent crime (let alone use a gun in said engagement) in the first place.

That is: you're arguing that wet streets cause rain.