The young women, many of them from poor families in Thailand, were promised trips to the United States. They would also receive visas. But the promises, the federal authorities say, came with an enormous toll: The women were required to work as prostitutes in cities all over this country until they could pay off exorbitant bondage debts." Law enforcement authorities on Thursday announced federal sex-trafficking conspiracy charges against 21 people, part of what they described as one of the most elaborate ... sex-trafficking operations they had seen. The operation had gone on for at least eight years, netted tens of millions of dollars, and involved hundreds of women. "The women ... were modern-day sex slaves," an indictment unsealed on Thursday in Federal District Court in Minnesota said, laying out criminal counts against a long list of defendants, including conspiracy to commit sex trafficking, sex trafficking and conspiracy to engage in money laundering. [United States attorney] Gregory Brooker ... described the ring as "a multimillion-dollar, modern-day organized crime operation." While still in Thailand, the women were usually told that they would work as prostitutes, the indictment said, but the terms of the deals shifted substantially once they arrived in the United States. Threats were made. Bondage debts suddenly skyrocketed. Some women were even told to have plastic surgery to make them more "appealing" to customers, then ordered to reimburse the cost of surgery as part of their ever-growing debt.