Complex sentence: With the advent of Prohibition, the North Side Gang took over the formerly legal breweries and distilleries in that part of the city and start producing bootleg alcohol and became one of the most powerful gangs in Chicago.
Split into simpler sentences: With the advent of Prohibition, the North Side Gang took over the formerly legal breweries and distilleries in that part of the city and start producing bootleg alcohol. They quickly became one of the most powerful gangs in Chicago.