In 1967, New York City eliminated license requirements for massage parlors. Many massage parlors became brothels. In 1970, Nevada began regulation of houses of prostitution. In 1971, the Mustang Ranch became Nevada's first licensed brothel, eventually leading to the legalization of brothel prostitution in 10 of 17 counties within the state. In time, Mustang Ranch became Nevada's largest brothel, with more revenue than all other legal Nevada brothels combined. By World War II, prostitutes had increasingly gone underground as call girls.