In his 1963 inaugural address, then Alabama Governor George Wallace issued his infamous salvo, “Segregation now, segregation tomorrow, segregation forever!” His prophecy turned out to be a delusion. But although Wallace’s cherished social institution has since expired, his battle flag has endured. More than 40 years after Wallace wrapped his candidacy in the Confederate flag, the rebel X continues to inspire devotion and repulsion across the country.

In his comprehensive new book, “The Confederate Battle Flag: America’s Most Embattled Emblem” (Harvard University Press, 448 pages, $29.95), John M. Coski chronicles the rich history of the so-called second American flag. Throughout, Mr. Coski, who is a historian and library director at the Museum of the Confederacy, offers an “explicitly relativist” approach that attempts to validate the flag’s various interpretations.

Yes, the flag memorializes the troops who fought for the Confederacy. Yes, it provides symbolic shorthand for states’ rights. Yes, it calls to mind the atrocities committed under Jim Crow. And, yes, it epitomizes a certain frat-house decor. “It is a fundamental mistake to believe … that one’s own perception of a flag’s meaning is the flag’s only legitimate meaning,” he writes. “People must not impose their interpretation of the flag on others.”

The author begins by clarifying the flag’s origins. In 1861, the Confederacy’s Provisional Congress appointed a committee to help create a new flag for the new nation. Eventually they settled on a design, dubbed the Stars and Bars, which resembled the Stars and Stripes. But early in the war, during a battle at Bull Run, a group of southern troops mistook the two flags and fired on their compatriots. Following the battle, General Pierre Gustave Toutant Beauregard began advocating for a unique battle flag, one that had been designed by William Miles, the committee’s chairman.

Miles had taken a South Carolinian secession flag – featuring an upright blue cross, studded with 15 white stars, set against a red background alongside a palmetto tree and a crescent – and revamped it. First, he had stripped away the fussy ornamentation. Then, at the request of a Jewish acquaintance who objected to flag’s overt Christian symbolism, Miles had tilted the cross into the now familiar X. Mazel tav! Thus the Confederate battle flag was born.

The flag grew in popularity and gradually eclipsed the Stars and Bars as the de facto Confederate flag. Southern troops loved to fly it, and Yankees loved to tear it down. The author notes that, of the 2,100 Medals of Honor handed out during the Civil War, more than half were awarded for capturing the enemy’s flag. One soldier who received honors later recounted in his memoir that he had picked up a flag, which other soldiers had ignored, “because I thought it was pretty, and I wanted to have me made a shirt out of it.”

We hear you, buddy.

Over the years, the Confederate emblem has spread out from flags to T-shirts, to neckties, to beach towels, to bumper stickers. Sex sells in America. And so does the Confederate flag. Witness, for instance, the creators of “Dukes of Hazzard,” who in the 1980s racked up more than a $100,000,000 in annual sales of merchandise bearing the flag’s emblem.

The peak of Confederate chic, however, actually occurred three decades earlier. In 1950, the Confederate flag swept across the Mason-Dixon Line and began decorating front porches from California to New York. Cultural observers were baffled by the craze. “Don’t ask me why,” wrote a contributor in the NAACP’s magazine, The Crisis. “Sometimes it’s little green lizards, sometimes it’s birds-on-a-stick. Now it is Confederate Flags.”

The fad lasted for roughly two years. But shortly thereafter, with the advent of the civil-rights movement, the flag’s evolution towards benign meaninglessness took an ugly turn. Southern segregationists hoisted the flag in hatred and intimidation at countless civil-rights protests. Beginning in the 1960s, civil-rights advocates began targeting the flag as a racist symbol. Southern heritage groups, in turn, rallied behind the flag.

The antagonism, the author notes, has been raging in a perpetual cycle ever since. “If precedent serves as a guide to the future, insults hurled at the flag and demands for its removal will prompt more people to rally to its defense,” writes Mr. Coski. “The Confederate flag is not an alien symbol grafted onto the American tradition and is not therefore simply going to disappear.”

In other words: The Confederate flag now, the Confederate flag tomorrow, the Confederate flag forever.

Although Mr. Coski succeeds at cooling down much of the overblown rhetoric that tends to swirl around the flag, his own writing can be somewhat stifling. Too often, the book’s narrative droops listlessly. Mr. Coski is also a relentless researcher: Throughout, he is able to revive his story by passing along a plethora of surprising stories, anecdotes, economic statistics, and editorial quotations regarding the flag. As a result, Mr. Coski’s book is ultimately worth reading.

Mr. Coski’s meticulously researched book boils down to a simple truth: The Confederate flag means different things to different people. And whatever that interpretation happens to be, chances are, it’s already summarized on a T-shirt. Mr. Coski recounts how after the release of Spike Lee’s 1992 film “Malcolm X” people began sporting X-inspired clothing – to which Southern heritage groups offered a sartorial response reminiscent of Mr. Coski’s own relativism. “You have your ‘X’,” read the shirts. “And I have mine.”

Mr. Gillette last wrote in the pages on academic fraud.