What statement best describes the impact of the African slave trade?

What statement best describes the impact of the African slave trade?
 
  a. It had little impact upon the number of wars in Africa.
  b. It reduced the number of wars in Africa because all the African states united against the European slavers.
  c. It increased the number of wars in Africa because of the increasing demand for prisoners who could be sold as slaves.
  d. It died out with the discovery of the South Asian Spice Islands.
  e. It was carried out peacefully as wars or violence would reduce the number of slaves and thus profits.