Given the enormity and longevity of the Atlantic slave trade, how important was it to modern history? Why do you think it happened?

Assignment instructions HIS325b:
Source of Reading: Robin D. G. Kelley and Earl Lewis’s To Make the World Anew: A History of African Americans and any additional readings related to the discussions and questions below.
Discussion: Explain the reasons for and historical ramifications of the Atlantic slave trade.
Based on your readings respond to the following:
Given the enormity and longevity of the Atlantic slave trade, how important was it to modern history?
Why do you think it happened?