I knew a woman who was a perfect example of how this sort of thing happens..
She was a Vietnamese girl who met an Aussie in Vietnam, and was swept off her feet by promises (the usual kind..a nice home, his family would love her like a daughter, lalala) but when she got here, the family - who lived on a farm in outback QLD - wouldn't allow her in the house. She had to sleep in sheds that also housed the dogs. She was treated like servant, spoken to like dog, allowed no money of her own, had to do all the cleaning and chores or she wouldn't get basics like meals or toiletries, and wasn't allowed to eat with the family.. MInd you, she wasn't so 'low' the son wouldn't have sex with her. In the shed, of course. Threats and fear kept her from seeking help, as well as sheer distance. She wasn't allowed to drive any of the cars.
Anyway, she finally stopped being afraid of these people -- shot her 'husband' in the leg, stole his car, and drove across the country...
When I met her, she had a job and (I am guessing) citizenship. w/e, I feel she'd earned it. But yeah, that's how slavery happens.