I don't pretend to know what the explanation is, but this is a phenomenon observed all over the western world. For whatever reason, blacks are uniquely prone to violent criminal behavior.

Well when you start looking at other variables besides race you do get a more clear picture. Population density is a stronger predictor of crime than race is - and ethnic minorities are far more likely to live in areas with high population density. So is income/social class. Educational attainment... the more factors you consider the more you realize the correlation with race doesn't mean as much on it's own. And yes many of those factors are because of historical policy, even if they are different from country to country. The UK has so many ethnic minorities concentrated in densely populated cities because that's where the demand for foreign workers was. The US has that because of the "Great Migration" and the movement of African Americans away from the rural South and into America's urban areas. The policies and histories are different but coincidentally had some similarities in outcome. I mean think about it logically, people who are raised on a farm aren't ever going to get involved in gang violence.