On July 3, 1930, President Herbert Hoover signed the appropriation bill for the Boulder Dam. The dam was later renamed the Hoover Dam during the Truman administration. Work started on the dam in 1931 and Las Vegas' population swelled from around 5,000 citizens to 25,000, with most of the newcomers looking for a job building the dam. However, the demographic of the work force consisting of males from across the country with no attachment to the area created a market for large-scale entertainment. A combination of local Las Vegas business owners and Mafia crime lords helped develop the casinos and showgirl theaters to entertain the largely male dam construction workers.