The play A Doll's House, by Henrik Ibsen, is a realistic drama whose main character, Nora, is an upper-middle class wife and mother that has not yet found herself as a person. Nora Torvald is a woman of her generation: Someone who fulfills the societal expectations of marrying a man of good status, and then becoming a nurturing and loving mother.
However Nora goes beyond those expectations: She also puts on an act of joy, naivete, fun, and excitement whenever she is front of her husband. It is easy to perceive that Nora puts on this act mostly for the sake of getting her husband's attention, his acceptance, and most importantly, his appreciation.
This leads to the main idea of the play: Expectation versus Disillusion. Nora's need for attention, acceptance, and appreciation is too great to realize that what she gets from Torvald is not appreciation, but merely superficial feedback. When things really get tough, and their marriage is put to the test, we see how Torvald fails the test miserably.
When Nora makes the shady deal with Krogstad to obtain money to save her husband's life from illness, she believes that all the entertainment and joy she has given her household will eventually compensate for the shaky nature of the deal she makes.
Right when the truth about the deal comes to light, and Nora expects Torvald to understand, he commits the ultimate act of deception: He turns his back on her, undermines the sacrifice she had to make, and basically treats Nora worse than a career criminal.
This leads to the second main theme, which is fantasy versus reality. When Nora is faced with Torvald's reaction, she realizes that her entire life has been like a play put on for Torvald's entertainment. She is his doll, living in the dollhouse he provides for her.
This triggers the end of everything: Nora realizes that she is nobody's doll. She is nobody's savior, either. She has been used and, for that reason, it is her turn to move on and leave that life of lies behind.
But you neither think nor talk like the man I could bind myself to. As soon as your fear was over—and it was not fear for what threatened me, but for what might happen to you—when the whole thing was past, as far as you were concerned it was exactly as if nothing at all had happened. Exactly as before, I was your little skylark, your doll, which you would in future treat with doubly gentle care, because it was so brittle and fragile. [Getting up.] Torvald—it was then it dawned upon me that for eight years I had been living here with a strange man, and had borne him three children—. Oh, I can't bear to think of it! I could tear myself into little bits!
There are the reasons behind the most important themes in the play.