In a U.S. town, a mining company owns all the stores and most of the houses. It sells goods to the workers at inflated prices, offers house rentals for twice what a mortgage would be, and makes sure to always pay the workers less than needed to cover food and rent. Once the workers are in debt, they have no choice but to continue working for the company, since their skills will not transfer to a new position. This situation most closely resembles:
child slavery
chattel slavery
debt slavery
servile marriage