The main conflict in A Tree Grows in Brooklyn is the main character’s struggle with her own poverty. The Nolan family’s poverty is the root of all other conflicts in the novel: for example, the struggle between Francie’s parents, Francie’s struggle to obtain an education, and her struggle with her own self-image and her relationship with her family.
Francie’s parents, Katie and Johnny, were doomed from the beginning due to Johnny’s alcoholism and inability to provide for his family, thereby leaving the burden to his wife and two children. In the third book of the novel, Johnny’s death and the birth of Francie’s youngest sibling, Annie Laurie, sink the family deeper into economic strife despite Katie Nolan’s careful financial planning.
Francie’s ongoing struggle to obtain the education she desires is hindered not only by her poor economic standing, but also by her poor relationship with her mother, who prefers her younger brother and decides to send him for further schooling when the family can only afford to send one child. Francie is also forced to join the work force in order to support her family instead of furthering her education.
Ultimately, class is reinforced not only by the Nolans’ economic situation, but by the people around them. It is reinforced when Francie visits an upper-class doctor for vaccination, and he says,
Filth, filth, filth, from morning to night. I know they’re poor but they could wash. Water is free and soap is cheap. Just look at that arm, nurse.
Francie is mortified by the comment and thinks herself “a dirty girl” because of it, internalizing the doctor’s class bias against the children he is meant to treat. Even the nurse, whose own roots reside in Brooklyn, chooses to sympathize with the doctor instead of Francie due to the shame of poverty. In the end, Francie’s own struggle with her poverty is resolved when her mother manages to marry a wealthy man, and the Nolan family leaves their Brooklyn home behind.