There are approximately 1 million blacks currently incarcerated (federal, state, AND county). Now add: the number who have been in prison but are now out of prison (including released due to court order re: overcrowding); the number who have “gotten off” due to prosecutorial incompetence or “deals” or jury incomptence (think “OJ”); the number who are convicted but are on-the-run fugitives; and finally the number who haven’t been caught and convicted and have so far gotten away with crimes. Four million, easy.
The biggest contributing factor to imprisonment is the war on drugs.
http://en.m.wikipedia.org/wiki/United_States_incarceration_rate