I would say who because it is calling for them in the context of who because they were just mentioned.
The break down of traditional boundaries in the face of increasingly global financial and cultural trends.
By producing a significant number of an item the production cost of said item decreases, thus leading to a larger profit margin.
- I hope this helps :)
Spanish colonies needed many workers because they needed to grow their crops, mine gold and silver, and work in their new cities. Spain wasn't able to have enough Spanish workers so they ended up taking Indians as their slaves, giving them very little food and water forcing thousands to die of starvation and overwork.
