Fwiw, there wer about 4 million slaves in 1860 per the census. If you want to put a pen to paper and ballpark some numbers (obv that wouldn't cover everyone ever enslaved in the 80 years of us government.
On topic, it's an incredibly stupid idea to make the people of today pay for the wrongs of others, just as its stupid to reward people for wrongs committed against their ancestors. There is no end to wrongs committed by our government against specific groups of people, and reparations would further the injustice not aid in curing it. It's a slippery slope and has a very occutard hue to it.
What makes this so libtarded is the blaming of government for the shortfalls of one segment of society, while simultaneously looking to it to make things right. These people should be small government brownbackites, in essence the victims of the most egregious form of cronyism, instead they want the punitive government to lash out at some other undeserving group of people, as if that will solve a problem rather than creating more. So bizarre to acknowledge the source of the problem, then demand a bigger, stronger, more powerful problem.