Why and how do authors use flashback?

Flashbacks interrupt the chronological order of the main narrative to take a reader back in time to the past events in a character's life. A writer uses this literary device to help readers better understand present-day elements in the story or learn more about a character

Explanation:

the civil rights act was passed on april 9, 1866 by a republican dominated congress. it was passed over president johnson's veto, in an effort to push back against discrimination of african americans.