Organized crime in Chicago boomed in the 1920s during Prohibition, as criminal organizations saw an opportunity to profit massively from the illegal alcohol trade. This led to intense rivalries between groups like Al Capone and Bugs Moran, culminating in the bloody 1929 Valentine's Day Massacre that left 7 of Moran's men dead. The mobs used weapons like Tommy guns and shotguns to enforce their control and protect lucrative speakeasies. When Prohibition ended in 1933, the mob activity declined dramatically as their main source of illegal income dried up.