Who did europeans turn to for labor? why?

They turned to Africa for slavery. Here's why:

labour to work the gold and silver mines and tobacco plantations
-criminal and outcasted slaves from Europe, or indigenous had perished, turned to Africans for labour force
-Africans had certain level of immunity to some tropical diseases. They had experience and skills in metal-working mining and tropical agriculture
-African rulers who provided the captives
-Main source of people for sale into slavery was those captured in warfare
-primary motive of these wars was the formation and expansion of states
- rarely sold ppl from their own society, except unwanted criminals and outcasts