When “Angels in America” premiered on Broadway in 1993, The New York Times’s Frank Rich called it “the most thrilling American play in years.” Tony Kushner’s two-part epic about American life, set against the AIDS crisis and Ronald Reagan’s presidency, quickly became, by consensus, one of the 20th century’s most essential works of theater. (The play is coming back to New York, at the Neil Simon Theater, beginning previews this month and opening in March.) In 2016, Slate published an oral history of the show, in which Mr. Kushner and more than 50 others talked about the production’s long and often difficult road to success. Now the authors of that history — Isaac Butler, a theater director himself, and Dan Kois, an editor and writer for Slate — have published a new book that expands on it: “The World Only Spins Forward: The Ascent of ‘Angels in America.’” The book covers the development and life of the play, as well as Mike Nichols’s adaptation of it as a mini-series for HBO in 2003. Below, Butler and Kois talk about the influence of the political climate on their book, a film adaptation of “Angels” that never came to pass and more.

When did you first get the idea to write this book?

DAN KOIS Isaac and I were conducting interviews for the Slate story in spring 2016. We kept getting so much amazing stuff. Every single person we talked to would tell us the kind of story you tell about the defining artistic and intellectual moment of your life. No one was like, “Oh yeah, it was great. I don’t remember much about it.” One week, we each interviewed members of the original cast. I interviewed Kathleen Chalfant …

ISAAC BUTLER and I interviewed Ellen McLaughlin. And at some point in that interview — which was 2 ½ hours long; not what I thought it was going to be — Ellen said, “You might not have realized this yet, but you’re actually working on a book.” I told Dan, “Ellen said this very charming thing on our phone call.” And Dan said, “Chalfant said the same thing to me.” As in many things, Ellen and Kathy were right.

KOIS Both of us, in our late teens or early 20s, came out of “Angels in America” transformed politically and artistically. I had always assumed, and heard thirdhand, that it had an appropriately epic origin story — technical drama and legal drama and angels falling from the sky. And that seemed like a story that ought to be told.