During the early part of the 20th century, the temperance movement was successful in passing the 18th amendment to the United States Constitution, which made the manufacture, sale, or transport of intoxicating liquors illegal. Less than 15 years later, the 18th amendment was repealed by passage of the 21st amendment. Although there are a number of laws which regulate the manufacture, sale, and consumption of alcohol in the United States, alcohol has remained legal since passage of the 21st amendment.
In order to understand the purpose of the 21st amendment, the history of the 18th amendment must first be visited. During the beginning of the 20th century, a movement which would become known as the temperance movement took root. The temperance movement in the United States began back in the early 1800s as a predominantly religious and moral philosophy. Members of the temperance movement believed that over-indulgence in alcohol was detrimental to both the physical and psychological health of an individual. In the beginning of the temperance movement, the philosophy was simply "temperance" — not abstinence — which meant consuming in moderation.
By the turn of the century, the movement had gained momentum for a number of reasons. The country was recovering from the devastating effects of the Civil War. In addition, many women became very vocal opponents of alcohol and the effects it has on marriage and the family. Anti-alcohol education had even made its way into many school curriculum. By 1917, an amendment was proposed that would completely ban the manufacture, sale, or transportation of any "intoxicating beverage."
The proposal was passed by both the House of Representatives and the Senate in December of 1917, beginning a period in US history known as Prohibition. Interestingly, the 18th Amendment did not actually ban the consumption of alcohol. Instead, it simply made it impossible to purchase alcohol legally, which eventually led to a huge black market for alcohol.
The practical result of the 18th amendment was that jails were full past capacity, as otherwise law-abiding citizens were made into criminals as they purchased underground alcohol or manufactured their own. This created a lucrative business for actual criminals, since the demand for alcohol did not diminish despite the ban. Many criminals earned lots of money transporting the illegal liquor throughout the country.
The 21st amendment, therefore, was finally proposed in February of 1933, which called for the repeal of the 18th amendment. Many of the states were still fearful of the political power held by the temperance movement, which led to ratification of the 21st amendment by state convention instead of state legislatures, thereby allowing the politicians to remain neutral. The state convention method allows the registered voters to decide, rather than the legislators, and has only been used once for ratification of the 21st amendment. The amendment was adopted in December of 1933 and, as of 2011, remains the only amendment to repeal a previous amendment.