The main action of Giants in the Earth centers of the conflict between Per and Beret Hansa. While Per dreams of building success for his family in America, Beret cannot adapt to the new environment. One of Rölvaag's primary goals in the novel is to realistically portray the struggles and hardships of the pioneering immigrants in America. This exploration offers Rölvaag an opportunity to rethink the frontier myth of nineteenth-century America. In the spirit of manifest destiny in America, the pioneer settlers saw the frontier West as the embodiment of opportunity, possibility, and optimism. The frontier myth celebrated the American West as a "promised land" where the settlers could live happily ever after. Rölvaag overturns this myth, detailing the daily life of the settlers in order to debunk the fairy tale of the frontier as a land of instant prosperity. Early in the novel, as the characters build sod homes and toil the land, Rölvaag shows that the prairie is a brutally real place, not a mere mythical conception. As an immigrant himself who knew first-hand the difficulty of building a new life on the prairie, he realistically chronicles many of the hardships that the pioneers face. Throughout the novel, the characters battle the elements of nature (storms and a plague of locusts), their own psychological demons (Beret's depression), and each other—conflicts that represent the lengthy catalog of challenges that many immigrants faced.
Giants in the Earth is not a celebration of American manifest destiny; instead, it is a tragedy that reveals the human cost of the immigrant experience. Beret, who embodies this cost, represents the antithesis of the frontier myth; she is unable adapt to life in the New World and longs to return to her native Norway. She feels homesick throughout the novel, as she does not enjoy living in America and fears the unknown perils lurking on the prairie. Beret's depression and mental illness and Per's death represent the sacrifices the immigrants made to achieve their dream in America.
In his novels, Rölvaag is primarily concerned with immigration. In Giants in the Earth he explores the cost of this immigration, showing that success in America does not always compensate for the loss of a homeland. Indeed, loneliness, displacement, and alienation were sober realities in the experience of millions of immigrants who arrived in the United States in the nineteenth century. The Norwegian immigrants in Rölvaag's novel feel displaced in America because they do not know the native language or possess any filial ties to the land. Some of the immigrants, such as Beret, are simply unable to adapt to their new land because, in their strange new land, they feel uprooted from everything once dear to them. Beret's homesickness, depression, and mental illness represent the psychological toil many immigrants suffered. Her psychological conflict appears to its full extent in the chapter "The Heart That Dared Not Let in the Sun," in which she remembers her home and family back in Norway.
Rölvaag himself deeply believed in the sacredness of one's heritage, and in his own life he taught Norwegian language, literature, and history as a professor in Minnesota. He appears to sympathize with Beret and her resistance to the increasing Americanization of her friends. When the Norwegian settlers learn English and decide to adopt more pleasing American last names, only Beret objects. The minister serves as another spokesman for Rölvaag's beliefs, preaching to the settlers that they should not forsake their past.
Per and Beret represent two opposing aspects of immigration. Per represents the hopes and optimism of the immigrants who dream of achieving success in America, the land of opportunity. Beret, on the other hand, embodies the cost of immigration in that she represents everything the immigrants lose coming to America. Through Beret, Rölvaag depicts the angst of uprootedness, the sense of loss and alienation immigrants suffer when they surrender themselves to a new culture.
The land is an important element in Rölvaag's novel, and therefore it is no surprise that the relationship between humans and the environment is a major topic of exploration. Throughout the novel, especially in the first pages of Book I and Book II, Rölvaag portrays the prairie as an important character and a powerful force—in fact, we may even argue that the prairie is the most important character in the novel. In narrative asides, Rölvaag frequently describes the landscape, emphasizing its vastness and desolation. The emptiness of the land haunts Beret the most she cannot bear the fact that on the empty prairie "there isn't even a thing that one can hide behind."