The main message of A Doll's House seems to be that a true marriage is a joining of equals. The play centers on the dissolution of a marriage that doesn't meet these standards. At first the Helmers seem happy, but, over the course of the play, the imbalance between them becomes more and more apparent. By the end, the marriage breaks apart due to a complete lack of understanding between them. Together in wedlock, the two are incapable of realizing who they are as individuals. They'll don't know how to act as equals.
The Helmers marriage fell apart due to an imbalance of power.
Ibsen's concept of a true marriage seems to be a union of equals.