The gap, in America, is huge. Blacks are more than 20 times more likely to murder than are whites or Asians. Why? The most often cited reason is poverty. It's also the least likely. According to research, science and the data.
Long article on the subject, from Noah Carl, writing a magazine I’d not heard of, Aporia.
The least likely is poverty. Which we know from the fact that Black homicide rates in poor African countries do not correlate with levels of poverty. I've driven the length of the African continent. The poorest countries are some of the safest. There, that's my anecdotal evidence.
I've long known about the Cultural reasons proposed. I would guess that's a large to,largish factor. Culture affects behaviour. Behaviour affects how you interact with people. Get angry and kill them? Or argue it out?
The Testosterone reason I've never heard of. Males have more T than women. They kill more than women. Still. The author gives this factor little weight.
IQ is clearly a touchy one. Is there a cross-racial correlation between IQ within a given ethnicity and homicidality? There would have to be so, inter-ethnically, not just intra-ethnicity, to give it any weight.
The sad thing is, it’s very, very difficult to discuss this issue calmly, especially in the U.S.. To the Left it’s “poverty wot done it”, and poverty is, of course, the fault of the white man. If you look for other reasons you’re a bigot. Sigh….