How can I write a movie script or screenplay about the topic of slavery?
Here's a suggestion: write the screenplay from the point-of-view of an African-American male born into slavery in Maryland in 1780. His parents can tell him about the American Revolution, and how some slaves even helped fight on the American side. Let this slave lead a long life. If you like, you can have him get married, but his family is separated via sales. Let him talk of slave revolts and rumors of slave revolts. Give him an understanding master who will tell him things of the outside world--for this, I guess he would have to be a domestic servant. Let the slave in our screenplay be around at the time of the Civil War, and finally, let him still be leaving at the time of the passage of the Thirteenth Amendment which freed the slaves. This would give the protagonist (the slave) a big view on history. He could even tell his life story through flashbacks to a member of the Freedman's Bureau in the late 1860s.
This would give a big view on slavery; I hope that the play is at least ten minutes long, because you would need that to incorporate all parts of the story. Of course, you can always edit the life story of the slave to whatever you needed.
You may want to check out this history of the revolt that has been depicted in murals. (The revolt on the Amistad)