Because of many reasons gangs, or mobs, became more prevalent in the 1920's. One reason was the passing of the prohibition law. The mobsters of the gangs would be the ones who controlled the sales of the alcohol between the maker and the buyer. This was a popular way for them to make their fortune. Others may have had some business in gambling or prostitution. Because people saw the crimes that the gangs were doing as a appealing more men and some women were lead into the mobster life style. There were so many gangs, and by extension crime, in America that by 1926 approximately 12,000 murders were committed in a year. These types of gangs continued to grow and new ones were created so fast and easily because the law enforcement was overwhelmed with the amount of crimes being committed. Most of the local officers were working on preventing and arresting the bootleggers and the owner of speakeasies.
Because of the numerous gangs and the limited space you could easily find your gang in a rivalry. If that gang decided that you need to be killed the murder would be calculated and precise with no mistakes. Unlike the gang shootings we see today. However bad the gangs were for the general public they wanted to hear about how they lived in luxury or the tails of what they might have done. By the end of the gangster ruling most of them were either in jail or dead. Killed by a rival gang or the law enforcement in a raid.