James Truslow Adams, in his book The Epic of America, which was written in 1931, stated that the American dream is "that dream of a land in which life should be better and richer and fuller for everyone, with opportunity for each according to ability or achievement. It is a difficult dream for the European upper classes to interpret adequately, and too many of us ourselves have grown weary and mistrustful of it. It is not a dream of motor cars and high wages merely, but a dream of social order in which each man and each woman shall be able to attain to the fullest stature of which they are innately capable, and be recognized by others for what they are, regardless of the fortuitous circumstances of birth or position." (-215)
In terms of what the novel says about American identity, there are a few threads you could pick up – one is Nick’s comment in Chapter 9 about the novel really being a story about (mid)westerners trying (and failing) to go East : “I see now that this has been a story of the West, after all--Tom and Gatsby, Daisy and Jordan and I, were all Westerners, and perhaps we possessed some deficiency in common which made us subtly unadaptable to Eastern life” (). This observation suggests an American identity that is determined by birthplace, and that within the American identity there are smaller, inescapable points of identification.