That’s an interesting question. People like to blame guns, but

The United States’ homicide rate of 3.8 is clearly higher than that of eg France (1.0), Germany (0.8), Australia (1.1), or Canada (1.4). However, as per the FBI, only 11,208 of our 16,121 murders were committed with firearms, eg 69%. By my calculations, that means our nonfirearm murder rate is 1.2. In other words, our non-firearm homicide rate alone is higher than France, Germany, and Australia’s total homicide rate.

That’s from here, which is an interesting but long discussion of the topic:

https://slatestarcodex.com/2016/01/06/guns-and-states/

https://slatestarcodex.com/2016/01/10/guns-and-states-2-son-of-a-gun/

Edit: I’m not saying guns aren’t part of the explanation, but they don’t appear to account for the majority of the difference.