When the Spaniards (spain) and the Portuguese (portugal) came over to the new world, they brought many diseases that they were immune to but the Indigenous people were not. So many of these Indian's were dying because they were being exposed to disease like the small pox and measles. So these European people did not benefit from this journey when it came to getting free labor workers (slaves) *EXTRA NOTE* the spaniards were very vicious and cruel to many of the people (so were the Portuguese) but you can look up documents and see how they chopped apart babies and mothers and did terrible things to the women and the men
So they made there way over to Africa a very NOT advanced area (technology speaking). They were still using bow and arrows while the Europeans had firearms. So they took advantage of these powerless, un advanced people
hope that helped :)