Thomas Sowell discusses this extensively in a few of his books. One of the most prominent studies he discussed was a post-WWII longitudinal research study conducted on children born in Europe vs. those born in the US that came from either mixed race or black households. Many American soldiers stayed behind in Europe, started families with the women in those countries, and their children went through the education systems of those countries much the same way any black child would in America.
The results showed that black and mixed race children in Europe showed no difference in intelligence from their white counterparts while American black and mixed race children were markedly less intelligent than their white peers. This led Thomas Sowell to theorize that American culture and educational systems treat blacks differently than white counterparts (he does discuss segregation as a cross-section but doesn’t blame it outright), but what was interesting is that he points the finger at BLACK culture as the detractor vs. any sort of systemic racism.
Black culture in America has been the downfall of blacks, and race baiters continue to force the victimhood mentality down their throats to their detriment. There are few prominent blacks who are brave enough to stand up to their peers and say they need to clean up their own house, because it’s just too easy to play victim.
I believe welfare, with its breakup of black families is the main cause.
I think so too, and it's been enabled and reinforced all around.
"Acting white" is a thing. So is "thug culture." These are cultural norms.
Act out, get called on it, and blame the critic.