Answer:
when America had just been colonized, people from England or wherever they were coming from would not have enough money to pay to come over to America. so they struck a deal with the captain the deal was that the captain would bring people over to America free of charge, but, the people would serve the captain for months sometimes even years to pay back the captain. after they finished paying off their servitude, they were free to go. a slave on the other hand would be brought from Africa by force and they couldn't leave unless they were sold to someone that would let them go.
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