How is exploitation shown in A Doll's House?

It would be a bit too easy to assert that A Doll's House is simply about the exploitation of women—of both Nora and her friend Mrs. Linde. These two find themselves, as with women in general of that period, in subservient positions and are trapped by the social roles they must play. Nora, despite leading a comfortable bourgeois life, is under the thumb of an insensitive, domineering husband. At the same time, a constant threat hangs over her: she fears that Krogstad will reveal to her husband her "crime" of having forged her father's signature to obtain money that was needed for Torvald's medical treatment years earlier. Krogstad exploits the situation for leverage in obtaining a job that rightly should go, as Torvald intends it, to Mrs. Linde. The male characters exploit the social system and gender roles of the time (which, to an extent, still exist today, 130 years later) to achieve their goals.
Nora and Mrs. Linde are unable to break out of the roles assigned to them without undergoing huge sacrifices—Nora leaves her wealthy but abusive husband, and Mrs. Linde has to submit to Krogstad to get him to back off from revealing Nora's forgery to the authorities. In some sense the women can then be said paradoxically to exploit the weaknesses of the male characters. Torvald is completely destroyed by his own tyrannical outburst at Nora. He loses both her and (if he has enough insight to realize it) his own self-respect by going into a panic at the possibility of Krogstad's revealing Nora's "crime" to the police. Krogstad himself has been manipulated (and justifiably so) by both women. So in the end, the social tables are turned and Nora and Mrs. Linde do, in fact, overcome the exploitative situation in which they have been placed by the norms of their time.