Why did Jurgis and Ona's family decide to go to America?
Essentially, the promise that America held for immigrants like Jurgis and Ona was the reason they decide to come to "the land of opportunity." Jurgis and Ona recognize that their life in rural Lithuania holds little in way of economic or social promise. Jurgis is animated by the idea of starting a new life with Ona in the new world. Through she is devoted to her family, Ona recognizes the promise and possibility of a new life, in both economic and personal terms, through coming to America. For both Jurgis and Ona, this dream of equality of opportunity is what drives him:
In (America), rich or poor, a man was free, it was said; he did not have to go into the army, he did not have to pay out his money to public officials,—he might do as he pleased, and count himself as good as any other men. So America was a place of which lovers and young people dreamed.
The combination of the mythological promise of America and the idea of being able to live together as young lovers seeking to "make it big," is what drives both of them to come to America. In this, a vision of the American Dream is conceived. Through this, the proverbial American nightmare takes hold.