Most of the differences in people of different races in terms of behavior can be explained by societal means. African Americans are raised with different values in their family and therefore explains most of the differences in their behavior.
I've known intelligent black people, I've also known dumb Asians. The biggest determinator in if you're going to have a high IQ is having an enriched environment. With quite a few African Americans they grow up in poverty, and the culture has less emphasis on getting an education, which leads poor prenatal care and inadequate parenting, and even education.
People tend to hang around with peers of similar cultural values, hence black people hang around with other black people, due to the environment, then a lot of them become gang-bangers because there's a higher rate of crime and less education in impoverished areas, and it makes that kind of lifestyle seem more normalized.
Also, African Americans have a significantly lower rate of depression than Caucasian populations, this is because African Americans are raised to show anger and express their frustrations, while caucasians are raised to internalize.
Tl;Dr most of the difference in IQ between races is due to environment, and people of African American heritage when raised in an enriched environment display similar IQ to caucasians raised in an enriched environment.