Why did the spanish start bringing african slaves to their new world colonies in the early 1500s?

The Native American population they had been using for slave labor died off in large numbers due to European diseases.

Source: https://quizlet.com/26818080/k12-us-history-unit-1-flash-cards/

The  pan-african movement  was an "emotional, cultural, psychological and ideological  movement  that began among the  african  dispora in the western hemisphere, for a closer  purpose, so that  african  people could feel secure, attain political, economic as well as psychological power visa vis other races or world regions" .