CHICAGO — Nearly seven decades ago, James Middleton was just a toddler when he watched a white man shoot and kill a black man in the little town of Lambert, Mississippi.

He had tagged along with his father to run errands and, giddy with excitement, sat in his daddy's Ford as they pulled up to a local restaurant. There was a commotion out front —a family friend arguing with the eatery's white owner, who had a pistol in his hand.

"You nigger!" Middleton recalls the white man shouting. "I'll kill you!"

The friend ran. Gunshots followed.

"I looked down and I could see this man, still trying to breathe, and blood was coming out of his chest," says Middleton. "I don't like to remember bad things. But it seemed like bad things were always happening to black folks."...