The book is about blacks those who think they are Jews.
Here's the description of the book:
Black Jews in Africa and the Americas tells the fascinating story of how the Ashanti, Tutsi, Igbo, Zulu, Beta Israel, Maasai, and many other African peoples came to think of themselves as descendants of the ancient tribes of Israel.
For centuries, colonialists, travelers, and missionaries, in an attempt to explain and understand the strange people they encountered on the colonial frontier, labeled an astonishing array of African tribes, languages, and cultures as Hebrew, Jewish, or Israelite. Africans themselves came to adopt these identities as their own, invoking their shared histories of oppression, imagined blood-lines, and common traditional practices as proof of a racial relationship to Jews.