How could A Doll's House be considered a modern drama?

Ibsen's A Doll's House was a landmark play of Social Realism. 

Prior to the opening of this drama, audiences viewed romantic vignettes that were offered as escapes, plays in which exciting romances and adventures took place. However, Ibsen greatly altered this expectation by introducing Social Realism into the Victorian theater. For, he focused upon the characters' roles in society, placing a searchlight upon such issues as personal independence and actions driven by conscience rather than...

Ibsen's A Doll's House was a landmark play of Social Realism. 

Prior to the opening of this drama, audiences viewed romantic vignettes that were offered as escapes, plays in which exciting romances and adventures took place. However, Ibsen greatly altered this expectation by introducing Social Realism into the Victorian theater. For, he focused upon the characters' roles in society, placing a searchlight upon such issues as personal independence and actions driven by conscience rather than social mores.

In A Doll's House, Ibsen examines the restrictions upon wives and husbands both. While Victorian women are allowed little domestic or financial freedom as they are subservient to their husbands; men, too, are trapped into roles where respect-earning behavior is demanded. But, the paradox of this society which demands such stringent adherence to roles is that there exists a false morality. For example, in Ibsen's play, Nora has stepped outside the boundaries of the role of Victorian wife by forging her father's signature on a loan so that her husband's health could be saved in Italy; similarly, because Torvald accepts his role as moral authority, he cannot forgive Nora her act of love; instead, he sees her forgery as a crime.

Nora and Torvald stand in contrast to Kristine and Krogstad, who both were made to act in certain ways in order to care for their families, also; nevertheless, they accept each other in their renewal of their relationship. But, Torvald cannot fully forgive Nora, and she can no longer be his doll. Likewise, Nora cannot forgive Torvald for his condemnation of her act of obtaining a loan falsely so that he would be saved from death by going to Italy and its warm climate. Therefore, Nora asserts herself and leaves Torvald and her children.

Henrik Isben examines what one interpretation holds as

...the irrepressible conflict of two different personalities which have founded themselves on two radically different estimates of reality. 

Certainly, A Doll's House is a modern play as it employs drama as a forum for social issues.