What caused the Civil Rights Movement to slow and splinter in the mid-to-late 1960s?

MUST use these sources Primary Sources Secondary Sources Martin Luther King, Jr., “Letter from a Birmingham Jail” (1963) Robert C. Weaver, “The Negro as an American” (1963) George C. Wallace, “The Civil Rights Movement: Fraud, Sham, and Hoax” (1964) Malcolm X, “Untitled Speech” (1963) Vanessa D. Murphree, “‘Black Power’: Public Relations and Social Change in the 1960s” Leon Litwack, “‘Fight the Power!’ The legacy of the civil rights movement