Why did the Trade Begin?
Expanding European empires in the New World lacked one major resource -- a
work force. In most cases the indigenous peoples had proved unreliable (most of
them were dying from diseases brought over from Europe), and Europeans were
unsuited to the climate and suffered under tropical diseases. Africans, on the
other hand, were excellent workers: they often had experience of agriculture and
keeping cattle, they were used to a tropical climate, resistant to tropical
diseases, and they could be "worked very hard" on plantations or in mines.