I predict slavery stumbles along until the 1950s when agriculture moves to mechanization. Still this greatly depends on if manufacturing can be profitable using enslaved labor. From 1930 until 1960 there was an increase in the use of mechanization in the agricultural industry, this would result in an excess in slaves unless manufacturing could absorb the excess slaves. As long as slave owners could make a profit using slave labor, slavery would limp along. The slave owners would not need to make a huge profit from enslave labor, any profit from slave labor would be acceptable, however, declining profit margin would decrease the influence of slave owners. \n\nSo starting in the 1950s to 1960s the United States is looking for a way to end chattel slavery. So with some form of gradual emancipation, and with some form of government paying slave owners to free slaves, I am thinking that slavery ends in the late 1960s to late 1980s.