Prohibition officially went into effect in January of 1920 and it was not long after that organized crime became involved in the illicit alcohol business. While the Roaring Twenties was known for many things, such as shifting cultural norms and a booming economy, the impact of crime and Prohibition came to define much of it.
Throughout the decade, crime syndicates provided speakeasies and secretive drinking establishments with smuggled and clandestinely produced beer and spirits. In many cities, a thriving underground culture developed around these establishments. The temperance movement which eventually resulted in Prohibition had its roots in the mid-19th Century. However, many people in the 1920s came to see imbibing alcohol as a rebellious and free-spirited activity that defined much of the culture of the period. In this sense, the Roaring Twenties can be seen as the beginning of a new cultural era and a rejection of past ethical stances.
As criminal organizations became increasingly involved in the business of producing and supplying illegal alcohol, levels of violence increased dramatically around the United States. The federal government was mostly powerless to put a stop to this. As violent crime rates rose, public opinion increasingly shifted against Prohibition. This opposition further fueled the counter-culture movement in the country. It also came to influence politics. As the decade reached its end and it became clear that Prohibition was a massive failure, many began lobbying for the repeal of the 18th Amendment, including presidential candidate Franklin Roosevelt in 1932.
When all this is considered, it can be seen that Prohibition and the resulting surge in organized criminal activity were a very significant part of the Roaring Twenties.