Fitzgerald was a realist, and his attention to detail in the novel is scrupulous and comprehensive in capturing the setting of the novel, the Roaring 20s in America. Throughout the novel, dozens of historical references can be identified, from World War I to the specific musical selections played at Gatsby's parties to the "fixing" of the 1919 World Series, and these are only a few. As a result, in addition to being one of the finest novels in American literature for its structure, style, and thematic development, it also stands, in many ways, as a historical document. Fitzgerald incorporated the contemporary and the historical into his novel because, most profoundly, The Great Gatsby is an examination of a particular time in America and its role in our history as a nation, as well as the story of the characters.
That being said, incorporating World War I into Nick and Gatsby's first meeting serves a purpose in plot and character development. Their friendship will become central to the novel, and in this first meeting, an immediate bond is established between them. They are both young men who served in the war. Also, many rumors about the mysterious Gatsby have been introduced into the novel, and his brief conversation with Nick about specific army combat units (Gatsby mentions the Third Division and the Seventh Infantry) provides for the first time some factual information about Gatsby's past.