Eugene O’Neill, the man who invented serious American drama — and who was never accused of brevity — would likely stare dumbfounded at the opening pages of John Patrick Diggins’s intellectually rigorous “Eugene O’Neill’s America” (University of Chicago Press, 266 pages, $29).

The way Mr. Diggins tells it, O’Neill was born on Page 18 and died on Page 29. The morphine-addicted mother; the stints at sea and in a sanitorium; the friendships with Emma Goldman, Hart Crane, and John Reed; the multiple wives; the anarchist leanings; the Nobel Prize and four Pulitzers; the son he didn’t meet until the boy was 11; the acquisition of Charlie Chaplin as a son-in-law; the three generations of suicide attempts (he and his mother failed, while his son succeeded) — all this and more is tackled in 11 pages.

Instead of what, when, and where, Mr. Diggins — a distinguished professor of history at CUNY’s Graduate Center — is far more interested in why. Many have written about the impact of playwrights like Ibsen and Strindberg on such masterworks as “The Iceman Cometh,” “A Moon for the Misbegotten” (currently being revived on Broadway), and “Long Day’s Journey Into Night,” to say nothing of more than three dozen other plays. Mr. Diggins focuses less on these influences and more on the philosophers who he maintains were most crucial in forming O’Neill’s fatalistic world view, one defined by covetousness, discontent, and what Tony Kushner has called “the inevitability of ambivalence, and its cost.”

Oswald Spengler, Ralph Waldo Emerson, and many, many other thinkers make appearances in “Eugene O’Neill’s America,” but Mr. Diggins devotes by far the most space in this enlightening if at times prosaic dissection of O’Neill’s political philosophy to the troika of Alexis de Tocqueville, Arthur Schopenhauer, and Friedrich Nietzsche. He uses these three to examine what he calls O’Neill’s “central theme of desire and its objects and obstacles.”

O’Neill claimed to have read Nietzsche’s “Thus Spake Zarathustra” at least once a year and said it had “influenced me more than any book I’ve ever read.” Both writers, one a lapsed Catholic and the other an atheist, looked to Schopenhauer for insight into why so many people turned to religion. And Mr. Diggins shrewdly conflates the concepts of “will to life” (which Schopenhauer believed trumped reason) and “will to power” (Nietzsche’s twist on the idea) with Tocqueville’s belief that the ethos forged by democracy “is itself dominated by its passion for dominion.”

Heady stuff, and Mr. Diggins presupposes that you know your Hobbes from your Hegel. (It’s telling that “Ah, Wilderness!” O’Neill’s only comedy, receives far less attention than any other major work and several minor ones.) Rather than focus on “Long Day’s Journey” and “Misbegotten,” which many scholars read as glorified (if hardly abbreviated) Cliffs-Notes to O’Neill’s family life, Mr. Diggins begins and ends his book with a meticulous analysis of “The Iceman Cometh.”

This mammoth work, the last play O’Neill lived to see staged, is steeped in what Schopenhauer called “the terrifying certainty of death” and features as its protagonist a sort of nickel-beer superman named Hickey. Set in 1912, the year a 29-year-old O’Neill attempted suicide, it is made up of characters who “are beyond desire,” Mr. Diggins writes, “with no ends to live for and no causes to die for.”

“Iceman” hinges on the often illusory promise of the American dream, with its attendant disappointments. “They see it close enough to know its charms, but they do not get near enough to enjoy it, and before they have fully relished its delights, they die.” This quotation comes from Tocqueville’s “Democracy in America,” which Mr. Diggins describes as “a study in the tragedy of frustration.” (If anyone doubts the lasting impact of this condition, note the agonies of another, more recent Catholic of immigrant stock: When Tony Soprano’s therapist reminds him that the Founding Fathers guaranteed him not happiness but merely the “pursuit” of it, he grumbles, “Always a f***ing loophole.”)

The notion of discontent as a core component of American identity fed directly into what was by far O’Neill’s most ambitious project, a cycle of historical plays — the projected tetralogy ballooned into seven and finally 11 plays — spanning all of American history and collectively known as “A Tale of Possessors Self-Dispossessed.” O’Neill would ultimately dispossess himself of the entire project, casting the lot into a fireplace, but one entire work (“A Touch of the Poet”) and a substantial portion of another (“More Stately Mansions”) have survived. Mr. Diggins devotes a considerable stretch to these two and to the surviving synopses of the cycle’s other works. Along with his probing accounts of O’Neill’s incorporation of race and religion into his plays, this sequence offers the book’s finest synthesis of textual scrutiny and philosophical insight.

Perhaps Mr. Diggins’s affinity for this phantom project stems from the fact that most of it was never performed. Plenty of theater historians draw sustenance solely from the page, viewing actual productions as necessarily compromised. (Harold Bloom says he almost never enjoys seeing Shakespeare’s plays.) A similar reticence to engage with the plays as anything more than texts can be found in Mr. Diggins, who confines his analysis of almost every staging to a mention of whether critics and audiences liked or dismissed the work.

And yet he has dedicated “Eugene O’Neill’s America” to four of American theater’s pre-eminent O’Neill interpreters — the director José Quintero and actors Colleen Dewhurst, Jason Robards, and Paul Robeson. This would suggest that Mr. Diggins, who writes perceptively about minstrel shows in the context of racially themed works like “The Emperor Jones,” appreciates on some level the power of these works as staged entities.

Then why does so little of that appreciation make its way into Mr. Diggins’s book? If the philosophies on whose behalf he argues so fluently are, in fact, integral to the texts, mightn’t they emerge through the interpretive gifts of these four — or of any other performers or directors — just as surely as through textual citations?

The main reason this exclusion hurts “Eugene O’Neill’s America” is that O’Neill, more than any playwright I know of, demands to be heard and not seen. His endless recapitulations of the same melodies, his ludicrously elaborate stage directions, his shocking preponderance of exclamation points: All this makes actually reading an O’Neill work — as opposed to witnessing one, where the performers can modulate these aspects — a bit of a slog. Mr. Kushner once wrote that he could “make no claim for O’Neill as one of the great writers, only as one of the greatest playwrights; for these two things, writing and playwriting, are not the same, and O’Neill’s work makes that clearer than any other’s.”

By situating O’Neill’s work so resolutely on the printed page, Mr. Diggins has brought an inordinate amount of attention to O’Neill the writer. Quintero, Dewhurst, Robeson, and especially Robards forced a complacent and coddled America to acknowledge the greatness of O’Neill the playwright. And while it’s heartening that a book can now take such acknowledgement as a given, any discussion that ignores the plays as plays, no matter how cogent its philosophical arguments, takes O’Neill’s abilities too much for granted.