the entirety of the difference from its most comparable sibling nations being firearm homicides.

What? You mean to say that the U.S. having a higher income inequality, lagging education, worse health care, and higher incarceration rates, along with many other factors have nothing to do with this problem?

The United States has more in common with Mexico than we do the rest of the developed world. Of course our homicide rate is going to be much higher than the developed world, and I'd wager that our guns are vastly overshadowed by our other enormous problems.