I saw it firsthand in Illinois, the staggering racial bias of prisons; in that state, blacks make up 13 percent of the total population but represent 76 PERCENT of those incarcerated.
In the USA the drug laws are on the face of it color-blind and levels of drug-taking by whites and blacks are at equal levels. However the rules are selectively enforced and selectively prosecuted so that blacks are far more likely to be charged, sentenced and imprisoned.
This has led to a New Jim Crowe of mass incarceration of black people, at far higher levels than in apartheid South Africa, so that the USA today, under Obama, is, objectively speaking an institutionally racist state and something akin to a racial caste system has been built in America.
Michelle Alexander explains this in detail at in this lecture on selective enforcement: