The brutality of working conditions in Brazil, on the other hand, meant that slaves were never able to increase their population naturally, hence the continued need to import slaves into Brazil until slavery ended in the 1880s. So I noted earlier that slavery isn't new. It's also a hard word to define. Like Stalin forced millions to work in the gulags, but we don't usually consider those people slaves. On the other hand, many slaves in history had lives of great power, wealth, and influence. Like remember Zheng He, the world's greatest admiral? He was technically a slave.