when did the europeans start using africans as slaves?

[Tim D]

Rome (and other European city-states) used slaves in many occupations to build the empire, these were captured as a result of military campaigns and through commercial expeditions to take any populations that were outside the Roman Empire, a proportion of these were African. Although slavery existed long before, and since, Rome's predominance I believe they were the first Europeans to use a substantial number of African slaves.
Heman's agenda-based rant is far from accurate, slaves were imported into South Africa by the Dutch – not taken from South Africa by the British, who did not claim sovereignty of South Africa until 18 years before passing the Slavery Abolition Act in 1833.