Augustus grooms James accordingly, deeding him eight slaves when he’s only 11 years old. Augustus arranges for James’ appointment to West Point where he forms a bond with his classmate, Ulysses S. Grant, and they become lifelong friends to Longstreet’s benefit.

Like Grant, Longstreet distinguishes himself in the Mexican War. Afterwards, in the 1850s, he advances his career in Texas, embroiling himself in a scheme to assimilate the Mexican province of Chihuaha into the U.S. as a slave state.

Following Fort Sumter, Longstreet defects to the Confederate army where he swiftly achieves recognition as an officer’s officer. He excels at the Seven Days battles in Virginia in 1862 and becomes Robert E. Lee’s “senior subordinate” — Lee calls him “the staff in my right hand.”

When Yankee and Rebel forces converge at Gettysburg in 1863 and the Union takes the high ground, Longstreet pleads with Lee to fall back to more advantageous terrain, repositioning Confederate troops between the Union army and Washington, D.C.

Lee rejects Longstreet’s proposal and, on the fateful third day, orders the “Pickett’s Charge” assault. A wall of Yankee cannons and rifles explodes. “When the smoke cleared away,” Longstreet will write, “Pickett’s division was gone.”

In the war’s final year, Longstreet is severely injured by friendly fire, yet he returns for the surrender at Appomattox, where he helps achieve relatively favorable terms for the South from Grant.

“In exchange for their pledge that they would never again take up arms against the United States, Confederates would effectively be set free,” writes Varon. “Grant believed that generous terms were essential to pacification.”

High-ranking officers like Longstreet — he’s known as “Rebel No. 3″ — must appeal to the president for a pardon, which Grant eases along.

As one might expect, Varon writes, “Longstreet was a true believer in the Confederacy’s racial politics.” Up to end of the Civil War, “He evinced no willingness whatsoever to accept emancipation as a positive good or consider the possibility of Black citizenship.”

But, the author continues, “More so than any other prominent Confederate, Longstreet accepted the war’s verdict as final,” and he “would pivot very quickly to building a future for himself and his family in the restored Union.”

He establishes a cotton brokerage firm and insurance business in New Orleans. He becomes the port’s surveyor of customs, appointed by Grant, and he immerses himself the city’s “unique racial politics.”

Declaring his support for Reconstruction in 1867, he works to build Louisiana’s Republican Party, joining Afro-Creole leaders promoting education, transportation and voting rights for Blacks — a visionary “biracial politics” he comes to see as the “key to rebuilding the South.”

But the backlash to Reconstruction in Louisiana is violent, climaxing in the famous Canal Street Coup of 1874, a firefight in which Longstreet leads “interracial New Orleans Metropolitan Police and the state militia” against the “White League, the Democratic Party’s white supremacist paramilitary arm, full of Confederate veterans.”

He’s savaged in the Southern press, labeled “the blackest of all traitors.” The “Mobile Daily Tribune” regrets that his Civil War wound “was not mortal.”

As the myth of the Lost Cause materializes, the weird cult of Robert E. Lee develops, and Longstreet is cast in the role of Satanic adversary to Lee’s “faultless saint.”

For decades, he engages in a hot war of cold words with the former CSA general, Jubal Early, a bloodthirsty fanatic and bitter nemesis, who, in falsifying the record of Longstreet’s performance at Gettysburg, mounts a largely successful campaign that influences several generations of gullible historians. In a wonderful irony, it will be a work of historical fiction, Michael Sharra’s “The Killer Angels” (1973), that restores Longstreet’s martial stature irrevocably.

After New Orleans, Longstreet returns to Georgia, builds a house near Gainesville and purchases the town’s Piedmont Hotel. (A remnant survives today as headquarters for the Longstreet Society.)

For the rest of the 19th century, in a “tireless campaign of self-reinvention,” he pursues a wild career path: ambassador to Turkey, U.S. marshal and federal railroad commissioner.

He forges an unlikely alliance with New South boosters at the Atlanta Constitution, who share his advocacy of “economic modernization.” (They remain deaf to his calls for racial solidarity.)

He publishes his massive tome, “From Manassas to Appomattox: Memoirs of the Civil War in America” (1896) and devotes the final years of his earthly tenure to North-South reconciliation events, landing boots-up in 1904.

“Longstreet’s story,” Varon concludes, “is a reminder that the arc of history is sometimes bent by those who had the courage to change their convictions.” If imperfect in his struggle to vanquish the hyper-racist demon of his rustic youth, he was, at his best, steadfast and bold in dissent, and herewith he became one of the white South’s first modern men.

NONFICTION

“Longstreet: The Confederate General Who Defied

the South”

by Elizabeth R. Varon

Simon & Schuster 516 pages, $35