The gangsters of the 1920' and the mafia ruled the streets during that time. Many gangster's sold alcohol and liquor. They also made alcohol. Italian gangsters ran the streets of America in the 1920s. Irish gangs did too, also.
Many Italian mafia's made alcohol and sold it. They sold the alcohol to many speakeasies. Speakeasies were illegal bars where alcohol was being served. The Italian mafia's were making a lot of money because of this. But they were also causing crime.
When the gangs grew in the 1920s so did the violence in America. Many mafia's and gangs had gang wars. Many innocent people died because if this and were injured. Because of prohibition, this allowed the gangs to grow even more. And also prohibition allowed speakeasies to become more common. (http://alliance.ed.uiuc.edu/cdrom/hononegah/Mafia_Folder/Mafia.htm)