The 1920's is perhaps the most ironic of periods in American history. With the passing of 18th Amendment and the Volstead Act creating the Prohibition, which was supposed to reduce crime but only served to usher in a period dominated by organised crime and made millionaires and celebrities out of the most vile and violent low-life's the country had to offer - Al Capone, Bugsy Siegel, "Lucky" Luciano and Arnold Rothestein, to name but a few. In the novel it's alluded to that Jay Gatsby is a bootlegger just like Capone and Luciano, and the character of Meyer Wolfshiem is a clear allusion to Arnold Rothestein, as both are rumored to have fixed the World Series.
It is in this period that people started to notice the cracks in the American Dream and started to doubt the ideals, on which America was founded - if you work hard, you could earn respectability and a decent living, just like the character of Richard Hunter did in Horatio Alger's novel Ragged Dick. This cultural zeitgeist is captured at the heart of Great Gatsby, the most obvious example being George Wilson, who works hard in his garage but never manages to move beyond his blue-collar origins, which when contrasted with Gatsby's astronomical rise in fortune through bootlegging, shows clearly the cracks in the American Dream. As Jefferson once warned, America has become corrupted by the city, it has gone from a place of discovery, individualism and pursuit of happiness, to a materialistic, morally corrupt, greed obsessed culture typified by the gangsters of the time, and one that looks the same today as it did back then.
Featuring a character who fixed the World Series, further highlights the corruption of America, because if the All-American sport could be tainted by greed and crime, then how long before this corruption consumed every aspect of American life. The effects of the "Black Sox Scandal" of 1919 can still be seen many years after, the 1989 film Field of Dreams (70 years after the scandal) features ghost of the Black Sox, in particularly Shoeless Joe Jackson, looking for redemption for their crimes in rural America, as if that was the only place they possibly could escape the corruption that had tainted them and kind find America again, paralleling Nick's flight from the city and return to the Midwest at the end of the novel.
Perhaps by highlighting the corruption of the American Dream, is the reason gangster films, such as The Godfather, and TV shows such as The Sopranos, and Prohibition era Boardwalk Empire (featuring historical figures such as Lucky Luciano, Arnold Rothestein and Al Capone) have remained a prominent part of American culture to this day - 2012 saw release of Lawless and Killing Them Softly, and 2013 sees the release of The Gangster Squad.
While it is undeniably a love story, it is in its depiction of the decline of the American Dream and the corruption of America that transforms The Great Gatsby into a Great American Novel.