Congress passes the Mann Act, also known as the White Slave Traffic Act, which was ostensibly aimed at keeping innocent girls from being lured into prostitution, but really offered a way to make a crime out of many kinds of consensual sexual activity.
The outrage over "white slavery" began with a commission appointed in 1907 to investigate the problem of immigrant prostitutes. Allegedly, women were brought to America for the purpose of being forced into sexual slavery; likewise, immigrant men were allegedly luring American girls into prostitution.
The Congressional committees that debated the Mann Act did not believe that a girl would ever choose to be a prostitute unless she was drugged and held hostage. The law made it illegal to "transport any woman or girl" across state lines "for any immoral purpose." In 1917, the Supreme Court upheld the conviction of two married California men, Drew Caminetti and Maury Diggs, who had gone on a romantic weekend getaway with their girlfriends to Reno, Nevada, and had been arrested. Following this decision, the Mann Act was used in all types of cases: someone was charged with violating the Mann Act for bringing a woman from one state to another in order to work as a chorus girl in a theater; wives began using the Mann Act against girls who ran off with their husbands. The law was also used for racist purposes: Jack Johnson, heavyweight champion of the world, was prosecuted for bringing a prostitute from Pittsburgh to Chicago, but the motivation for his arrest was public outrage over his marriages to white women.
The most famous prosecutions under the law were those of Charlie Chaplin in 1944 and Chuck Berry in 1959 and 1961, who took unmarried women across state lines for "immoral purposes." Berry was convicted and spent two years in the prime of his musical career in jail. After Berry's conviction, the Mann Act was enforced only sparingly, but it was never repealed. It was amended in 1978 and again in 1986; most notably, the 1986 amendments replaced the phrase "any other immoral purpose" with "any sexual activity for which any person can be charged with a criminal offense."