During the Era of Prohibition (1920-1933) the Mafia/Gangsters became more powerful beacuse they saw a way to earn big money selling alcohol illegally. They were know as "bootleggers" because they smuggled the liqouor in their boots. They developed illegal underground bars called "speakeasies" because you had to whisper a password to get in. Inside the bars there was gambling and prostitution. Due to the great demand of alcohol the illegal bars were very successful for the Gangsters.
One of the most famous gangsters was Al Capone. He was in charge of running the underground alcohol business in the city on Chicago. Based on some records it was found out that he was making approximately $60,000,000 from bootlegging liquor, he also made $10,000,000 from racketeering. This was when gangsters threatened shop and business owners with violence unless they paid them money for so-called "protection."