Just a nit:

How many blacks living in America are descended from slaves, and how many are recent immigrants from the Carribbean and Africa?

Actually, a very high percentage of recent immigrants from the Carribbean are descendants of slaves. Slavery is why blacks were brought to the Carribbean in the first place. The slavery experience for their ancestors may or may not have ended sooner than for American blacks, but is just as real.

As for recent immigrants from Africa, some of them have much more recent experience with slavery. As hard as it is to imagine, slavery still exists in parts of the world, such as the Sudan. In many other parts of Africa, the issue isn't slavery but warfare. There are many recent immigrants who have firsthand experiences that I would wager had a far more profound impact on them than slavery that ended over a century ago here in the US. Sadly, stories like The Lost Boys of the Sudan aren't uncommon.