sentences:  After the arrival of the Portuguese in Brazil, the Native Americans started to trade their prisoners, instead of using them as slaves or food, in exchange for goods.But the enslavement of Europeans could also occur, as happened with Hans Staden who, after being set free, wrote a book about the customs of the Native Americans.The colonization effort proved to be a difficult undertaking on such a vast continent, and indigenous slave labor was quickly turned to for agricultural workforce needs.