I told you: white men from the South. Before 1890, the overwhelming majority of the nation's black population was in the Southern United States, where murder rates and rates of gun violence have far exceeded murder rates elsewhere since even before the Civil War.
Conflict resolution is cultural. White Southerners were far quicker to use violence as a way to settle disputes - often over nothing more than perceived slights - than their counterparts elsewhere. Many black Southerners adopted this behavior because they lived for generations under an economic and political system that was not possible without violence. So yeah, black Americans learned violence from their former white masters. And when they were chased out of the South they took their conflict resolution behaviors with them.
Also worth noting that many of the places where violent crime persists are where there's chronic poverty. Being poor doesn't make you commit violence, but a person who is poor and unskilled and feels that things won't change will probably feel like he has less to lose. People with less to lose are more likely to commit homicide than those who have something to lose, like a career, reputation, or time with family. It's no secret that systemic racial apartheid has deprived many black neighborhoods of resources and wealth that would make these crimes less common.
