First, even though it reduced crime at the beginning of its ratification, it was impossible for the American government to enforce the law. Many people got alcohol illegally, some people distilled alcohol at their own homes. Other people imported alcohol illegally into the country from neighboring countries such as Canada and Mexico, but a great portion of illegal alcohol came from Britain.
Secondly, instead of lowering crime and violence, it increased dramatically. This was all due to "organized" crime, since alcohol was no longer available to the public, these people had to turn to gangs to obtain their liquor. The high demand for alcohol and the low supply of illegal liquor led to the rise of many gangs. New York was where the most powerful gangs were located, but Chicago was the headquarters for the most famous gangsters. The most infamous and well known gangster was Al Capone.
Prohibition encouraged criminal activity instead of exterminating it.