The 18th Amendment
The groups dedicated to encouraging temperance had a number of reasons for it. They believed there to be a direct link between alcohol and many antisocial behaviors, like child abuse and domestic violence. Another famous concern was that of Henry Ford, who believed that alcohol had a negative impact on labor productivity.
Anti-German sentiment during World War I helped catapult the issue into law. Many of the nation's breweries were operated by German immigrants, also known as "alien enemies" by the Anti-Saloon League. The sentiment was that the grain being produced should be used to feed soldiers rather than produce alcohol.
Many others fought this growing issue tooth-and-nail. The Association Against the Prohibition Amendment and the Women's Organization for National Prohibition Reform were just two of these groups.
Despite the efforts of anti-prohibition groups, support gathered for a ban on alcohol, and Congress passed the 18th Amendment on Jan. 16, 1919 (it went into effect in 1920). The amendment prohibited the manufacture, sale, export, import and transportation of alcoholic beverages — but stopped short of banning personal possession and consumption.
Basically, if your wine cellar was already stocked, you didn't have much to worry about. The 18th Amendment brought to a national level what was already accepted in many states. Sixty-five percent of the country, including 19 states, had already banned alcohol on a local level.
The Volstead Act, or National Prohibition Act, was crucial to the success of the 18th Amendment — it provided the federal government with enforcing ability. It also defined criminal penalties, exceptions (medicinal and religious-ceremony use) and the alcohol levels that qualified as "intoxicating." Any beverage with more than 0.5 percent alcohol was over the legal limit.