Sexism
Torvald represents what he himself calls the "true man's heart." but the play reveals a false heart attached to on the other hypocritical expectations hand, Nora represents the masses of women who have given up their identities. Among them is the belief that women should accept a lesser status and value than men.
From the beginning of the play, the sexism is clear. Nora acts while Torvald, her master, lords his power over her in every detail. Ibsen reveals the reality of sexism: Torvald sees that women have no life outside of what their men tell them to have. He can't see Nora's own person or own thoughts, wants and need.