Henrik Ibsen's A Doll's House is generally considered to be modern drama, as was the drama of Germany's Bertolt Brecht. With these two gentlemen, drama was changed extensively yet again (as it had been changed by Shakespeare, Marlow, etc., during the Elizabethan Renaissance).
Some critics go on to note that Ibsen's work is considered "liberal tragedy" (while Brecht's work is associated with "historicized comedy"). Change was coming, and some modernists began to reject the realist movement. With advances in science and technology, literature in the old style was considered outdated—failing to keep up with the new world emerging.
...political, and economic forces were at work that would become the basis to argue for a radically different kind of art and thinking.
However, Ibsen did not completely reject the realist movement. He embraced the cause of human rights, though his work was first assumed to be written in support of the feminist movement. He was clear in explaining that he wished to draw attention to the struggles of "humanity" as a whole. His thinking is more contemporary as it addressed modern social problems and "social institutions."
Perhaps some elements of modernism are clearly visible in the plot of this (at that time) very controversial drama. At the end, Nora is devastated to learn that even while she was willing to sacrifice her life for her husband, he did not feel compelled to do the same for her. Audiences in Norway and Germany were appalled that Nora would leave her husband because this was seen as a completely unnatural behavior.
Ibsen is known as the "father of modern drama" because he elevated theatre from entertainment to a forum for exposing social problems.
The Romantic tradition in drama gave way to Ibsen's more "realistic portrayal of...characters" and their "psychological concerns"...within society. Ibsen is credited to a great extent to developing this more contemporary, "modern" drama.