You are correct. There's always been staggering levels of violence of blacks in northern cities. Even before the mass movement of blacks from the south to the north after WWII, the blacks in northern cities were known for their violent behavior and high homicide rates.
I wonder when the people at NR will apologize to John Derbyshire for speaking the truth? Unless there's a lot of police present, for their own safety the best thing for whites to do is to avoid large gatherings of young black people.
There are old FBI Uniform Crime Reports online from the 1950’s and earlier. The black homicide rate was much higher than white back then too.