> or is this another aspect of the US's unexpectedly high violence

That's a steep drop of context. The US doesn't have abnormally high violence overall, as your blanket statement would imply. The US has a lower rate of violent crime than Europe does and that has been consistently true for 50 years.

The US has an unexpectedly high murder rate due to the mass proliferation of easy to get handguns in its inner cities. If you remove that single factor, the US murder rate drops to something comparable to Canada. It's obvious that the murder problem in the US is a handgun problem and the stats always bear that out year after year.