It was the principal rival of the South Side Gang, also known as the Chicago Outfit, the crime syndicate of Italian-Americans Johnny Torrio and Al Capone.
It was during the Circulation Wars that future North Side leader Dean O'Banion, then a member of the juvenile satellite Little Hellions, would develop valuable contacts with politicians and journalists.
He also ran a publicity campaign in the North Side, with large-scale donations to orphanages and charities as well as food and loans to the poor and unemployed.
Although O'Banion was arrested and charged with burglary in 1922, the North Side Gang enjoyed considerable protection from the Chicago police department.
Attendees included Chief Detective Michael Hughes, Police Lieutenant Charles Evans, County Clerk Robert Sweitzer, public works commissioner Colonel Albert A. Sprague, and a host of both Democratic and Republican politicians.
In 1924, Chicago police assisted the North Side Gang in robbing the Sibly Distillery, which had been under federal guard since the beginning of Prohibition.
Escorted by Police Lieutenant Michael Grady and four detective sergeants, North Siders looted the distillery in broad daylight, taking 1,750 barrels of bonded whiskey worth approximately $100,000.
After his release from custody, Torrio acceded to demands from the Genna crime family, allies of Chicago Outfit, to kill O'Banion.
On 10 November, shortly after the death of Merlo, Frankie Yale, John Scalise, and Albert Anselmi reportedly entered the Schofield Flower Shop owned by O'Banion and shot him dead.
After the death of O'Banion, Hymie Weiss assumed leadership of the North Side Gang and immediately struck back at his rivals.
On 12 January, 1925, Weiss, Bugs Moran, and Vincent Drucci attempted to kill Torrio's lieutenant, Al Capone, at a Chicago South Side restaurant.
Moran then decided to kidnap one of Capone's trusted bodyguards, torturing him for information before finally executing him and dumping the body.
On 24 January, shortly after the assassination attempt on Capone had taken place, Weiss, Moran, and Drucci ambushed Torrio as he returned from shopping with his wife.
While Capone and his bodyguard were drinking downstairs, the North Siders drove by the lobby and opened fire with their Thompson submachine guns.
However, the primary target of the gunmen, Bugs Moran, leader of the North Side Gang, was not at the garage and escaped harm.
Known as the St. Valentine's Day Massacre, the attack effectively left the five-year gang war between Al Capone and Bugs Moran in a stalemate.
The brazenness of this crime resulted in a Federal crackdown on all gang activity in Chicago that eventually led to the downfall of both Moran and Capone.
The North Side Gang continued to control the 42nd and 43rd Wards and managed to thwart a takeover attempt by Frank McErlane in 1930.
Moran and the North Side Gang eventually lost control of their gambling operations to the new National Crime Syndicate.