For a New Historicist approach, you would want to examine the actual historical backgrounds to the ideologies displayed in the play. One good place to start would be the laws on banking and forgery. What documents would show what the actual reactions would have been to Nora's forging her husband's name? Were there any important newspaper stories that revolved around forgeries of family names? What sort of laws affected women's property?
For a Marxist approach, you might look at how the class and economic relationships of the characters determine the ways they think. In what way is the husband an exploiter of other people's emotional as well as material capital? Does his position as a capitalist determine the way he treats people as interchangeable objects? Does the exploitation and dehumanization of the worker under capitalism ultimately lead to a similar distortion of gender relations?