What were the "night men" trying to accomplish with their attacks?

Mr. Morrison tells a story which Mama doesn't want the children to hear, but to which Papa insists they listen. One Christmas during Reconstruction, Mr. Morrison was six and lived in a shantytown with his family. Night men came in pursuit of two teenage boys accused of molesting a white woman whom had hid in his house, hoping his strong father would help save them. Mama explains that slaves were bred for strength like animals during slavery. The night men burned and killed women and children, including his two sisters, and although Mr. Morrison's parents fought hard, they both died too. Though he was only a child, Mr. Morrison makes himself remember that night.