That's the thing, according to official stats the American black population has been VERY stable, constantly remaining at 12-13% since 1990. It's rather suspicious that the number hasn't changed in 30 years given the plummeting American white birth rates and the increasing black birth rates.
Also lately American blacks have became far more visible publicly, their representation in US media has grew tenfold, and none of the companies that pander exclusively to blacks (think shoe companies) haven't gone out of business yet, indicating that their consumer numbers are far greater than what official numbers convey.
Not to mention that during my travels I did not see a single place in America even close to 10-13% black, it's always a lot more. Sometimes hard to tell which flavor of mystery meat it is, but there's usually some black in there.