In Of Mice and Men the American Dream is symbolized by George and Lennie's desire for their own piece of land. They momentarily believe if they work hard and save their money, they can afford to buy a home and work only for their own upkeep rather than someone else's. Lennie and George's dream is eventually thwarted by the accidental killing of Curley's wife, demonstrating that no matter how hard one works, there are strong forces outside of one's control that ultimately determine one's success or failure.
Steinbeck has an eclectic cast of characters in the story that have noticeable differences, like mental or physical disabilities, that set them apart and influence how they are treated by others in society. Most specifically are Lennie, Candy, and Crooks, though Curley's wife can also be included because she is a woman, and therefore vastly different from the men around her.
In Of Mice and Men Steinbeck shows that hard-working Americans like George, Lennie, and the rest of their co-workers are unable to rise to a desirable middle-class lifestyle due to social and natural forces outside of their control. They are doomed to wander from place to place in search of better work, better pay, and a place to call home.
Curley's wife is the only female character physically present in the story. Her femininity is both feared and resented by the males that surround her on the ranch. Steinbeck uses Curley's wife to demonstrate how women are lonely and out of place in the masculine world of the ranch.
There is an ever-present sense of loneliness in the text. Crooks, Candy, and Curley's wife all express their deep desire for companionship. George and Lennie have managed to temporarily escape loneliness through their friendship, which makes others curious as well as a little jealous. George eventually ends up alone like the others after he is forced to kill Lennie at the end of the story.
Rabbits take on a significant role in the story, representing George and Lennie's vision of the American Dream. Before George kills Lennie, he tells Lennie about the rabbits that they plan to have. When George kills Lennie, he also kills the idea of the rabbits and their dream of having a life of freedom.
Crooks, the African-American stable hand, is the main example of how race is incorporated into the story. Steinbeck portrays Crooks as bitter and lonely because of the way he is ostracized from the rest of society. Steinbeck shows that despite African-Americans being free they are still enslaved by terrible racism in the United States. Curley's wife most poignantly reminds Crooks of his position when she threatens to have him lynched for crossing her.