Pretty much started with the president LBJ and his Great Society bill. They've been brainwashed into thinking that what happened 4-5 generations previous, is still owed to them. Now, pretty much the Democrats are using it as a tool for more votes. After all, it's not their money their giving away!!
I thought this all started with 40 acres and a mule? We shoulda picked our own dang cotton......... 
Actually, slavery as known in the south, was about to become obsolete. Yes, Eli Whitney's cotton gin was already operating..but further developments would have changed things...
Cyrus McCormick was producing the reaper as early as 1837..paving the way for further harvesting machines..
Sam Colt successfully demonstrated assembly line techniques..showing the way for mass production of farm machinery..
Perhaps by the beginning of the 20th century...many slaves would have been freed anyway..
However, this in no way justifies slavery, just helps to explain it's possible demise.
