To find books in the Phillips Library about History, you could look at the Library of Congress Classification Scheme. Once you know what the correct address is, you will be able to browse the shelves there to find more books that interest you.
African American History falls into the scheme at:
E184-185.98 Elements in the population
E185.2-185.89 Status and development since emancipation
E185.96-185.98 Biography. Genealogy
African American literature is classified under the individual author, including books by or about him.