Director Martin Scorsese and screenwriter Jay Cocks found their inspiration for Gangs of New York in Herbert Asbury’s 1928 book of the same name. According to Cocks, both he and Scorsese happened upon the text “independently of each other” over a Christmas holiday. They both fell in love with Asbury’s depiction of the city and were especially interested as this historical moment had received very little attention in film. They began working on the screenplay in 1976, but the film was not able to come to fruition for a number of years because of financial considerations. Scorsese and Cocks had actually already been planning on working together on a project after attending a screening of Sam Peckinpah’s The Wild Bunch in 1969 together. The film deeply impressed both of them and provided the inspiration for the western-style that Gangs of New York would come to employ.
While Herbert Asbury’s text served as the primary source for the film, the screenwriters and researchers utilized many others to enhance the historicity of the film. These included contemporaneous publications as well as histories written about the period after the fact. These resources were used to hammer down the details of 19th century New York City, such as the types of clothing people wore and what omnibuses and billiard tables looked like. The Rogues Lexicon, a dictionary of street and criminal slang published in 1859 as an instructional aid for the New York Police Department, was also used extensively to reproduce the language used in the streets of Five Points. The film did an impeccable job recreating the look and feel of 19th century New York. The film does receive some negative points, however, in how accurately it represented the finer historical points that it deals with. This was to be expected, to a degree, since the historicity of their primary source, Herbert Asbury’s book, has been routinely criticized from nearly the time of its publication.