I believe this is impossible to know as slave owners in the early days would not bother to record slave deaths any more than animal deaths; slaves were so disregarded. However, historians are taking the figure to be around sixty million. Imagine, huge numbers died on the march from their tribal homes to the coasts of Africa.
Then there were endless wars produced by the quest for new slaves. Millions more died in concentration camps before the sea journey, as well as from the terrible conditions on the boats. On arrival, weakened and cruelly treated, the work set them caused more deaths.
