Complex sentence: Whilst he was running the Writer's Group at the Royal Court, he began to teach that drama is about dominance and submission, and about people being changed by each other, a subject that previously had not been taught in the dramatic arts.
Split into simpler sentences: Whilst he was running the Writer's Group at the Royal Court, he began to teach that drama is about dominance and submission. It is about people being changed by each other, a subject that previously had not been taught in the dramatic arts.