A school district or public school academy that teaches world history in a middle school or high school grade is encouraged to focus the content of instruction regarding Africa on at least 1 or more of the following kingdoms: Ghana, Mali, Songhay, Benin, Bornu, Nubia, Axum, Meroe, Monomotapa, or medieval Ethiopia, or on the Swahili coast prior to 1750. This section is not intended to prohibit or limit teaching about other areas of African history.