What id Eugene O'Neill introduce to American Theatre?

Eugene O'Neill was a pioneering figure in American theatre, known for introducing a more realistic and psychologically complex approach to playwriting. He explored deep emotional and existential themes, often drawing from his own life experiences, which set the stage for modern American drama. O'Neill's use of innovative structure, character development, and poetic dialogue influenced countless playwrights and helped elevate the status of American theatre on the world stage. His works, such as "Long Day's Journey Into Night" and "The Iceman Cometh," remain foundational texts in the American theatrical canon.