The argument, restated, is that the particular historical experience of a particular group of people in relation to a colonizing power, may explain their role in the world today.
Would anyone blame the unemployment in the Palestinian territories and refugee camps solely on the Palestinians or would we also look at the external factors pertaining to Israeli aggression?
The proper analysis is not only looking at how the African American community is doing, but comparing it to the African diaspora as a whole, and that begins by looking at the effect of slavery and colonialism on Africa. Some economists have theorized that if it wasn't for Europen interference in Africa, the continent, as a whole, would be much more closer to the rest of the world.
Economist's View: "The Historical Origins of Africa’s Underdevelopment"
I have another journal that scrutinizes Africa region by region and concludes that those areas that were subjected to slavery and colonialism happen to be the most underdeveloped regions within Africa (and the world) as a whole.
Now, if the effects of slavery and colonialism on Africa can be empirically established, its not that much of a leap to conclude that Africans living in America, subjected to Jim Crow laws that only ended in the 1960s, may have economic, social, and political disadvantages.