Context: Numerous communities of dark-skinned peoples are present in North Africa, some dating from prehistoric communities. Others are descendants of the historical Trans-Saharan trade in peoples and/or, and after the Arab invasions of North Africa in the 7th century, descendants of slaves from the Arab Slave Trade in North Africa.

Question: Where was the Arab Slave Trade?
Answer: North Africa

Question: When were the Arab Invasions?
Answer: the 7th century

Question: Where were numerous dark-skinned communities? 
Answer: North Africa

Question: When did these communities begin?
Answer: some dating from prehistoric communities.

Question: Who are they descendants of?
Answer: Trans-Saharan trade in peoples