The Pacification of New York was a three-year-long process by which the Corleone crime family consolidated its control over New York City's criminal underworld, eliminating its smaller, unorganized gangs and leaving the American Mafia's "Five Families" in firm control of the city.
During the 1930s, the United States' largest cities were being born by underworld strife as ambitious hoodlums attempted to carve themselves empires. Newspapers and government agencies pushed for stricter laws and harsher police methods in the face of rising crime, causing established bosses like Vito Corleone of New York City's Corleone crime family to fear the suspension of democratic procedures. With his own empire secure, Corleone decided to bring peace to the warring factions in the city and nationwide. Throughout 1934, Corleone met with several New York gang leaders to propose spheres of influence and the creation of a confederated council, but too many special interests conflicted. Corleone decided that order and peace were impossible until the number of gangs could be reduced to a manageable number. Around five or six crime families would be allowed to exist, while the Black Hand extortionists, freelance loan sharks, and unaffiliated bookmakers would have to be eliminated. Corleone threw all the resources of the Corleone family against the gangs.
Initially, the war went poorly for Don Corleone, as a group of Irish stickup artists pierced the Don's protective cordon and put a shot into his chest; the assassin was immediately riddled with bullets. Don Vito's son Sonny Corleone stepped up to lead the Corleone family in its purge of the underworld, taking command of his own crew as a caporegime and showing a merciless ruthlessness during his urban warfare.
From 1935 to 1937, Sonny Corleone made a reputation as the most cunning and relentless executioner the underworld had yet known, eclipsed only by Luca Brasi, who went after the rest of the Irish gunmen and single-handedly wiped them out. After one of the six powerful families tried to interfere and become the protector of the independents, Brasi assassinated the head of the family as a warning. Shortly after, the Don recovered from his wound and made peace with that family.
The other families, namely the Barzini crime family, Cuneo crime family, Stracci crime family, and Tattaglia crime family, each vied for power, occasionally battling each other while carrying out regular gang attacks on Black Hand and Murder, Inc. hideouts and building factories, apartments, restaurants, and mansions as fronts for their criminal activities. Thai Yu's New York Tong and the Atlantic City entrepreneur Eugene De Luca partnered with various Mafia figures to preserve their own power.
By 1937, peace and harmony reigned in New York City except for minor incidents that ended in fatalities. Don Corleone carried his message through the United States, conferring with compatriots in Los Angeles, San Francisco, Cleveland, Chicago, Philadelphia, Miami, and Boston. By 1939, Corleone had achieved a working agreement amongst the most powerful underworld organizations in the country. The agreement covered only spheres of influence and an agreement to enforce peace in the underworld.