One characteristic of modern literature, including modern plays, is that it presents themes in which the characters struggle to accept traditional roles of authority, especially moral authority. One way in which Ibsen's A Doll's House falls under this category is that we see Nora questioning the authority of the law, her husband, and, by the end of the play, even God.
We see her question the authority of the law when she is first blackmailed by Krogstad. When Krogstad first points out Nora's fraudulent activity, she asserts that it was impossible to have obtained her father's real signature as he was dying at the time, and she could not have given up on getting the loan because the money was needed to travel to warmer climates so that her husband's health could recover. Krogstad then points out that he once committed the same act of fraud as Nora and for the same motive of saving his wife's life but that the "law cares nothing about motives" (I). Nora then argues that the law "must be a very foolish law" (I). Nora refuses to believe that she would not be entitled to any legal right to spare her dying father of any grief and to save her husband's life.
Towards the end of the play, Nora even begins questioning and refusing her husband's authority over her. After he "forgives" her for the fraud she committed once he learns that Krogstad will not press charges, Nora changes out of her costume into a day dress and commands her husband to sit down so that they can talk. Ironically, Torvald obeys her for the first time and actually does sit down. When Nora tells Torvald she is leaving and he forbids her, she even replies, "It is no use forbidding me anything any longer" (III). In addition, Nora asserts that she no longer believes that her most sacred duties are as a wife and mother; instead, she now believes that her most sacred duty is to be true to herself and to become "a reasonable human being" (III). When Torvald hears this, he demands of her, "Have you not a reliable guide in such matters as that?--have you no religion?," Nora's response is to say that she does not "exactly know what religion is" (III). Hence, Nora is not only rejecting her husband as her authority and moral guide, she is rejecting the religion her society holds true as her moral guide.
Therefore, we see that in rejecting authority and socially accepted religion as a moral guide, Nora is acting as a character that is characteristic of modern literature, making Ibsen's A Doll's House, a modern play.