Hey, I’m a geographer by training, inclination, whatever . . . so this story in the New York Times is very cool.  Think of it as a very early GIS (geographic information system) plotting social data (number of slaves) on a map so they can be read spatially.  Basically, it is an early choropleth map (odd the historian writing about this did not use this term*) where shading of different areas represents different concentrations of whatever is being measured (here, the percentage of the population of a given county that was enslaved).  You can see how this map presented information about slavery that made it easy to see that secession was about preserving a labor system (as opposed to more noble principles about State’s rights).
That said, the South was fighting for its life – it was already an agrarian, raw-material supplying cousin to the Northern states, dealing with massive income inequality and poverty issues.  Which should remind people of the situation in much of today’s developing world.  The Southerners who were wealthy needed slaves to stay that way . . . the entire South risked becoming, in effect, an underdeveloped area if slavery was abolished.  And if you look at post-civil war history, that is pretty much how it turned out.  Industry concentrated in the north until the Northeast moved on to biotech, education and other services, pushing the dirty production to the poorer South.  Now even that production is headed overseas.  That the Southern US is generally poorer and less educated (and therefore with fewer options) than much of the rest of the country is therefore not an accident, random or something inherent to Southerners themselves (my children are all Southerners, after all) – the South started off as a massively unequal raw material production zone, and it has been struggling with that legacy for the past 150 years.
And we expect countries that only emerged from colonialism 50 years ago to somehow do better?
*Geographers, why the hell is a historian writing our history, dammit?  We are better than this – surely we have covered a bunch of this already, but seriously, can we reclaim our disciplinary history from the people unclear on the concept of a choropleth map?
(h/t to Micah Snead)