Systematically screwing people for 300 years will do that to you, at least in the example of black populations
We can look at a place like the UK where there was no slavery, no "jim crow" type laws and see that blacks still continue to vastly disproportionate violent criminals.
Over half of detained boys from black or minority ethnic backgrounds
Blacks are arrested a 3x rate than white people
It's a culture problem (black culture is inferior to say, jewish culture) and the fact that blacks are naturally less intelligent than every other race in the world.