Between Melissa Harris-Perry , Ta-Nehisi Coates , Matthew Yglesias  and The American Prospect’s Adam Serwer , there’s been a great discussion on the origins of the American middle class, and the extent to which it was purposefully built to exclude African-Americans. To add to the conversation, I’ll say this: in addition to emphasizing the actual anti-black policies pursued by the federal government, it’s also worth noting the pervasive climate of anti-black violence that directly discouraged African-Americans from reaching above their “station.”
Lynchings, for example, were often used against blacks who emerged  as economic competitors to local whites, and overrall, the lynching rate was correlated with regional economic performance. When competition for jobs was low, lynchings declined, and when competition for jobs rose—particularly during economic downturns—lynchings increased. The same was true for outbreaks of mass racial violence; by and large, white supremacists targeted prosperous black communities for destruction. The Tulsa race riots stand as a prominent example, along with the Rosewood massacre of 1923 and the East St. Louis riots of 1917.
In other words, not only could you be killed for transgressing the nebulous and arbitrary social requirements of the Jim Crow, but you could also be killed for starting a business, accumulating wealth and otherwise trying to improve your situation. Together with state and federal discrimination against blacks, you had—until the middle of the twentieth century—a country where the government worked to prevent black economic advancement, with an assist from widespread violence from private actors. With few exceptions, this predicament was unique to African Americans, and a critical part of understanding the “wealth gap” as it developed through the twentieth century and into the present.
Unfortunately, this is one of those things that doesn’t have a place in the public conversation, in part because most Americans either can’t or won’t imagine an America where—if you were the wrong color—pulling yourself up by your bootstraps was punishable by death.