Did the early Europeans destroy much of the African art because they considered it idolatry?
This is a question that would deserve a very long answer, because the subject is quite complex. The bottom line, though, is that a lot of African art has been destroyed by mssionaries because they thought is was idolatry (and it represented the religion they wanted to replace with Christianism). Something similar can be said, however, about the role of Islam in Africa. There has been a study on that subject, which is quite balanced – even if it does not take into account the role of radical Islamists, which were not as influential in the 1970s as they are today (RenĂ© Bravmann: Islam and Tribal Art in Africa, 1974). Unfortunately, I do not know of any study that specifically deals with the impact of Christians on the destruction of indigenous African art. There are books on Christian art in Africa, though. furthermore, it should not be forgotten that a lot of African art was lost due to secular destruction and robbery (cf. Benin, Nok, Ife, for example).