The second girl did wonderfully, learning hairdressing and marrying a terrific man. But Srey Mom, it turned out, was addicted to methamphetamine and fled back to the brothel world to feed her craving.

Image Nicholas D. Kristof Credit... Fred R. Conrad/The New York Times

I just returned again to Ms. Khorn’s brothel to interview her, and found something remarkable. It had gone broke and closed, like many of the brothels in Poipet. One lesson is that the business model is more vulnerable than it looks. There are ways we can make enslaving girls more risky and less profitable, so that traffickers give up in disgust.

For years, Ms. Khorn had been grumbling to me about the brothel  the low margins, the seven-day schedule, difficult customers, grasping policemen and scorn from the community. There was also a personal toll, for her husband had sex with the girls, infuriating her, and the couple eventually divorced bitterly. Ms. Khorn was also troubled that her youngest daughter, now 13, was growing up surrounded by drunken, leering men.

Then in the last year, the brothel business became even more challenging amid rising pressure from aid groups, journalists and the United States State Department’s trafficking office. The office issued reports shaming Cambodian leaders and threatened sanctions if they did nothing.

Many of the brothels are owned by the police, which complicates matters, but eventually authorities in Cambodia were pressured enough that they ordered a partial crackdown.