The novel goes into it a little more. When Vito was first brought home from the hospital Sonny was determined to get some of the Family's street businesses (i.e. the numbers) back running again. When the mob war started the Corleones lost control of some of these businesses because they were busy protecting themselves and fighting off the other Families. In Harlem, for instance, the blacks were formerly "runners" but became bankers in their own right when the war started. Tom Hagen told Sonny the blacks would not voluntarily go back to being runners again. Sonny's answer was to loosen Clemenza's regime on them.

Its further written that there was no problem in getting the rackets back from the blacks because the police would not accept any payoffs from blacks then because of racial distrust.