What are the main themes in Ibsen's A Doll's House?

There are many themes in Ibsen's A Doll's House. 

Perhaps the most significant theme () is that of the absence of the female identity in the male-dominated society.

Years before, when Torvald Helmer became seriously ill, the only way his life could be saved was if they travelled to Italy so he could recuperate. At that time in society, among many other restrictions, women could not take loans. So Nora, his wife, did the only thing she could—she secretly forged her dying father's signature and took a loan from the disreputable and tragic figure of Krogstad.

In the course of the play, a desperate and lonely Krogstad angrily demands his money from Nora. When Torvald learns not only what Nora has done, but also that he is at the mercy of Krogstad, who holds the promissory note she forged, he lashes out at his wife and accuses her of being a "hypocrite, a liar...a criminal," with "no religion, no morals, no sense of duty..."

Though Nora wants to leave at that moment and take her own life to protect her husband, Torvald says that she is being dramatic and dismisses her intent. He brutally announces that they will live together as they always have—as far as polite society can tell—but that there is no love between them and that she will no longer be allowed to care for the children:

But you can't be allowed to bring up the children; I don't dare trust you with them—

When Torvald receives word that Krogstad has forgiven the debt and Torvald's reputation is saved, society's view of women is further clarified as he states:

You loved me the way a wife ought to love her husband. It's simply the means that you couldn't judge. But you think I love you any the less for not knowing how to handle your affairs? No, no—just lean on me...I wouldn't be a man if this feminine helplessness didn't make you twice as attractive to me.

By the end of the scene, Nora finally realizes that her husband does not value her as a person, but treats her like a child's doll in a playhouse, controlling her every move; she is also aware that during their entire marriage (like her father did with her before she married) he has also endeavored to control even her thoughts and opinions. Nora's resourcefulness in saving her husband's life and attempting to repay the loan does not matter to him at all.

Another theme (common in literature) is appearance vs. reality. While the Helmers appear to be the perfect loving couple, in truth their relationship is based upon Torvald's attempts to have absolute control of his wife. He treats her like a child—not as a woman, and not as an equal. His arrogance and pride have convinced him that no one else matters as much as he does: he cares more for himself than anyone or anything else.

HELMER:

Now you've wrecked all my happiness—ruined my whole future...I'll be swept down into the depths on account of a featherbrained woman.

When Krogstad's letter arrives, Torvald realizes that the danger has passed.

HELMER:

Nora! Wait—better check it again— Yes, yes, it's true. I'm saved. Nora, I'm saved!

NORA:

And I?

HELMER:

You too, of course. We're both saved.

While Nora gives the appearance of a dutiful wife, she secretly has broken the law (though she cannot understand that saving her husband by any means necessary would be illegal) and has deceived Torvald in many ways. For example, with money Torvald has given her for household expenses, Nora has cut corners and scrimped—even taking on part-time work to earn money—to repay the debt.

In the examples given, there are other themes that are also apparent, such as deception and betrayal. While Nora has deceived Torvald about the money she borrowed, he has deceived her in letting her believe he loved her "more than the world," more than life. When he is confronted with disaster, Nora discovers his lie. And while Torvald may see his wife's behavior as a betrayal of sorts (obviously he is oblivious to the truth that she saved his life), Torvald betrays his wife in refusing to support her as a husband should and turns on this woman he claims to love when he feels he is in danger. Worse than anything Nora can imagine is the knowledge that her children will be taken from her simply because she wanted to protect her husband: for Nora, this is Torvald's greatest betrayal.