This is not the case.

". . . the Lord Jesus learnt to walk, not on the continent of Europe, but in Mizraim (Egypt), in Africa. Secondly, when the Ethiopian eunuch, Chancellor of the Exchequer of Queen Candace, became a Christian while reading the prophet Isaiah chapter 53, and Philip helped him to understand what he was reading, the natives of the British Isles were only just in the process of being educated by the Romans to read and write. So let nobody tell you that the Gospel of The Lord Jesus Christ is a European invention." ~ Dr Konotey-Ahulu, renowned sickle-cell anemia researcher

Kwanzaa invented in 1966 by Marxist U.S. citizen, Ron Karenga, aka Dr. Maulana Karenga. Karenga was also a founder of United Slaves, a violent nationalist rival to the Black Panthers gang.  Kwanzaa's tenets align perfectly with Marxist tenets.

Christians were the ones who worked against the establishment to abolish black slavery.  It was the non-Christians and in-name-only Christians who fought the movement to free the slaves.  Unfortunately, slavery still is a problem in many non-Christian countries today.