In Chicago in the 1920s, life was controlled by the gangs throughout the city, specifically the North Side & South Side gangs, who had beef with each other. Throughout the 20s, the two sides had turf wars, bombings, and shootings, with each side trying to take full control of the city.
Eventually, the North Side Gang took it too far, and The Outfit decided to do something about it. But that lead to a lot of back and forth assassination attempts, which ended with a very bloody Valentine’s Day in 1929.