Throughout the narrative of The Great Gatsby there are allusions to East and West. Nick Carraway comes from the Midwest (Minnesota) to work in New York City; Gatsby, too, has come from the farmlands of North Dakota (Midwest). They both live at West Egg, "the less fashionable of the two, where the nouveau riche live; with East Egg reserved for the very wealthy such as the brash Tom Buchanan, or the haughty New England families of social prestige.
Across the courtesy bay the white places of fashionable East Egg glittered along the water...
This socio-economic divide of the two locations which otherwise resemble each other is depicted by the attitudes of Buchanan, the prestigious Sloanes,and the types who attend Gatsby's parties. In addition, the corruption of the East is symbolized by the Valley of Ashes, a grey industrial wasteland of New York City.
At the end of his narrative, Nick Carraway who finds Daisy's desertion of Gatsby and Tom's exploitation of him opprobrious, and he tells Gatsby that he is superior to "the whole damn bunch." Thus, in disillusionment, Nick considers the significance of his past and longs to return to the West as "the green breast of a new world," still a reflection of the American dream, as no values exist in the materialistic wasteland and white facades of the East.
Significantly, F. Scott Fitzgerald himself was born in St. Paul, Minnesota, and while he and Zelda lived in New England, he found the Easterners jaded, exceedingly materialistic, and dishonorable. So, Nick gives voice to Fitzgerald's perspective.