Prohibition
Prohibition in the United States focused on the manufacture, transportation, and sale of alcoholic beverages; however, exceptions were made for medicinal and religious uses. Alcohol consumption was never illegal under federal law. Nationwide Prohibition did not begin in the United States until January 1920, when the Eighteenth Amendment to the U.S. Constitution went into effect. The 18th amendment was ratified in 1919, and was repealed in December 1933 with the ratification of the Twenty-first Amendment.
Bureau of Prohibition
The Bureau of Prohibition (or Prohibition Unit) was the federal law enforcement agency formed to enforce the National Prohibition Act of 1919, commonly known as the Volstead Act, which elaborated upon the 18th Amendment to the United States Constitution regarding the prohibition of the manufacture, sale, and transportation of alcoholic beverages. When it was first established in 1920, it was a unit of the Bureau of Internal Revenue. On April 1, 1927, it became an independent entity within the Department of the Treasury, changing its name from the Prohibition Unit to the Bureau of Prohibition. In 1930, it became part of the Department of Justice. By 1933, with the Repeal of Prohibition imminent, it was briefly absorbed into the FBI, or "Bureau of Investigation" as it was then called, and became the Bureau's "Alcohol Beverage Unit," though, for practical purposes it continued to operate as a separate agency. Very shortly after that, once Repeal became a reality, and the only federal laws regarding alcoholic beverages being their taxation, it was switched back to Treasury, where it was renamed the Alcohol Tax Unit.