Which figure of speech is used in this text?
Go back to Mississippi, go back to Alabama, go back to South Carolina, go back to Georgia, go back to Louisiana, go back to the slums and ghettos of our northern cities, knowing that somehow this situation can and will be changed.
—Martin Luther King, Jr., "I Have a Dream" speech

 - anaphora
 - apostrophe
The text uses anaphora, the repetition of the same word or words at the beginning of several phrases or clauses.
King repeats the words go back at the beginning of each clause.