Mann Act
The act made it illegal to bring women or girls from one state into another for the purpose of "prostitution or debauchery, or for any other immoral purpose," which means for them to have sex for money. The law was there to stop human trafficking.  Most human trafficking was people taking young women from place to place for prostitution. The Mann Act was one of a group of laws about moral reform, during an era that was known as Progressive Era.