Throughout the novel, Lewis attacks the narrow-mindedness, mediocrity, and conformity of small-town America in the early twentieth century. Lewis's brand of social satire shocked American readers in 1920. Before the publication of Main Street, many Americans still viewed the small town idealistically, the last bastion of good people and traditional American morals and values in the midst of a changing and somewhat frightening modern world. In this novel, however, Lewis exposes this myth of the goodness of small town-life as a falsehood. He portrays the narrowness of small-town life in its rigid demand for conformity, its interest only in material success, and its lack of intellectual concern. Lewis paints a scathing portrait townspeople as suspicious spies rather than warm and trusting neighbors.
In painting this portrait, Lewis satirizes many small-town archetypes and institutions. For example, the women of the Jolly Seventeen, who represent the town's upper class, criticize Carol because she dares to be different from them. While Carol demands humane treatment of laborers and the poor, the others prefer to maintain the status quo. Suspecting anyone who does not conform to their standards, they unfairly expect Carol to dress like them, think like them, and talk like them. Lewis further satirizes the women of the Thanatopsis Club, the women's study club, because they believe that learning mindless facts—such as studying an author's life rather than his work—counts as intellectualism. The townspeople pride themselves on their Christian charity and great democratic spirit, but in reality express extreme prejudice against farmers, immigrants, hired workers, the lower classes, and German-Americans (during World War I). The townspeople reject Carol's reform ideas—even her simple suggestions of refurnishing the rest room for farmer's wives and establishing programs to support the town's indigents—because they oppose spending any money. Furthermore, the townspeople feign a strict moral code—they attend church and force Fern Mullins to leave town because she attends a barn dance with a student—but themselves commit secret transgressions and secret love affairs. In characters and institutions such as these, Lewis exposes the hypocrisy he sees in small-town America.
The main conflict of the novel stems from Carol's desire to change the town in the face of the town's resistance to such change. This conflict creates an atmosphere of hostility and suspicion that pervades the entirety of the novel. Though Carol is unable to bring about any radical changes to Gopher Prairie, she does partly triumph in the sense that she puts up a fight. She does not, unlike most of the other townspeople, mindlessly conform to Gopher Prairie's standards. Carol heroically tries to maintain individuality in a society that demands her conformity. She remains friends with many outcasts of the community, such as Miles Bjornstam, Fern Mullins, and Erik Valborg. As the heroine of the novel, Carol reflects the spirit of the Progressive movement in America in the early twentieth century, under the banner of which many people took an interest in social issues such as the labor movement and the suffrage movement. A career woman before she marries Kennicott, Carol reflects the position of the modern "emancipated woman." Reflecting the spirit of the Progressive era, Carol represents change. It is not surprising, then, that she finds herself out of place in Gopher Prairie, a place that steadfastly resists change. Carol opposes modern industrialization and materialization because they destroy the land's natural beauty and the spirit of adventure of the early pioneers. She feels that materialism has forced people to lose their sympathy and humanism. She rebels against the American standardization and uniformity and the exploitation of the farmers and laborers. Because Carol represents Lewis himself, she also reflects his own rebellion against his hometown.
Carol constantly struggles with disillusionment in the novel, in her marriage and in her interactions with the community of Gopher Prairie. While she romantically daydreams about turning Gopher Prairie into a beautiful, sophisticated place, she meets only opposition and gradually realizes that she cannot achieve any reforms. Lewis conveys her disillusionment brilliantly at in Chapter 3, in the scene in which she tours Gopher Prairie for the first time. The town does not correspond to Carol's preconceived image of the perfect rural village. Instead, she finds the place ugly and uncivilized. One of Carol's most important and painful lessons occurs when she learns of the pettiness and narrow-mindedness of the townspeople for the first time. Whereas she had believed that the townspeople warmly accepted her, she learns from her friend Vida Sherwin that in actuality they constantly watch and criticize her.
Carol also finds disillusionment in her marriage to Kennicott. She realizes that her husband is not her "Prince Charming" and often struggles with the realities and stresses of marriage. Furthermore, one of the most important passages of the novel, in Chapter 22, occurs when Carol finds all the traditional images of the small town in American literature to be false. Despite her frustration with Gopher Prairie, however, Carol also encounters disillusionment in her big-city stint in Washington, D.C. Although she believes she can escape Gopher Prairie and establish a new, exciting life in a big city, she realizes at the end of the novel that big life is not as exciting as she once fantasized, and that, even if it were, she is unable to fully escape the grasp of Gopher Prairie.
Carol's war with Gopher Prairie counterbalances her war with her husband. Just as Lewis realistically depicts life in a modern American small town, he also realistically depicts a modern marriage. Early in the novel, Carol realizes that her marriage is not a fairy tale. Although she loves her husband fondly, she catches herself fantasizing about a "Prince Charming" in Chapter 14. Although Carol and Kennicott clearly love each other throughout the course of the novel, they have about as much in common as night and day. We often wonder whether the two are really compatible. While Carol supports social reform and embodies change, Kennicott embodies Gopher Prairie's resistance to change in his preference for maintaining the status quo. While Carol yearns for what she considers beautiful and noble—noble architecture, Yeats's poetry, modern theater—Kennicott scorns what he sees as her highbrow attitude.