As a professor at Gettysburg College, Allen C. Guelzo has been positioned to scout the town and its surroundings as closely as anyone has ever done, even the soldiers who fought there and the authors who have written whole books about each turn in the three-day battle. He knows every street, every knoll and every gully. But his title at the college — director of Civil War era studies — makes clear that his franchise covers not just combat but everything about the war, and he exercises it fully in this rich, original work.

In a dozen previous books, such as his highly regarded “Lincoln’s Emancipation Proclamation,” Guelzo has studied the politics and philosophy of American history, focusing more on what happened in men’s minds than on the battlefield. In “Gettysburg,” he now brings Clausewitz’s truism that war is “the continuation of politics by other means” down to the personal level, strongly suggesting that even as the guns roar, individual soldiers’ politics will affect how they fight.

He presents Robert E. Lee as commander of a “Virginia-besotted army . . . a divided house in political respects” as it marches into Pennsylvania. Many officers from other states resented the fact that the choicest assignments went to Virginia generals such as A.P. Hill and Richard S. Ewell, and indeed resented the very name of the Army of Northern Virginia, since fewer than half of its troops were from Virginia. Guelzo happily chooses sides in these factional disputes, repeatedly sympathizing with those Southern generals who “suffered from being a non-Virginian” and with the Georgian who complained that “no matter how trifling the deed may be which a Virginian performs it is heralded at once as the most glorious of modern times.” When it comes to perennial arguments over who’s to blame for the eventual Confederate defeat, Guelzo has little patience with “postwar keepers of Lee’s memorial flame.”

There was even more infighting within the Union Army of the Potomac, where a surprising number of prominent soldiers are introduced as “McClellanites,” which implies softness toward slavery and lack of enthusiasm for the war. That list includes George G. Meade, who took command only three days before the battle and was later pilloried by Northern radicals for having planned to fight along a defensive line closer to Washington. Yet in the heat of battle, some of those McClellanites, such as Winfield Scott Hancock, were the fiercest fighters, and when it was over, Meade was the only general to have defeated the vaunted Lee.

Guelzo considers all the endless debates about who should have done what: Should Lee have heeded James Longstreet’s reluctance to attack head-on? Did Longstreet’s balkiness determine the battle? Would Stonewall Jackson, mortally wounded two months earlier, have made a difference? Where was Jeb Stuart? Guelzo often concludes that received wisdom is in error, that judging right and wrong is much simpler at this far remove than it was in the smoke and confusion of combat.

’Gettysburg: The Last Invasion’ by Allen C. Guelzo (Knopf)

Along the way, he tosses off references to now-obscure battles of history, as if anyone who reads his book is sure to be familiar with what Napoleon did at Wagram, the Russians at Inkerman and Zachary Taylor at Buena Vista. That display of his learning may sound annoying, but from him it isn’t; it’s his expansive, rolling storytelling that makes this book so engrossing and sets Guelzo’s Gettysburg apart from the many others. Witness how he slashes into one of the campaign’s most controversial figures:

“Dan Sickles belonged in a novel rather than an army. Corrupt and confident, he coruscated political charm, talked in the grandest of hotel manners, and oozed sleaze and dissimulation from every pore. . . . [He] was, from the beginning, a spoiled brat, and he matured from there into a suave, charming, and pathological liar, not unlike certain characters in Mozart operas.” Guelzo recalls Sickles’s 1859 revenge murder of Francis Scott Key’s son for seducing his wife and his pleading temporary insanity to escape conviction. Then Guelzo agrees with Harper’s Weekly: Sickles was “loved more sincerely, and hated more heartily, than any man of his day.”

What was about to happen to Sickles, who lost a leg on the second day, and to more than 50,000 other men who became casualties, seemed inconceivable as the armies wrestled into place about Gettysburg. As the first artillery rounds whooshed in, Henry L. Baugher, the president of Gettysburg College, optimistically tried to continue classes. Finally, when soldiers and excited absentee students clumping to and from the rooftop cupola made his efforts useless, he wearily adjourned and said, “We will close and see what is going on.”

With many such asides, Guelzo’s book enlarges the conventional battle narrative. There are nearly 500 pages between his prologue, which lays down the geology and human history of the land about Gettysburg, and his epilogue, which muses on each sentence of what Abraham Lincoln said there. Through those pages runs a thoroughly readable description of every hour of those three hellish days, in enough detail to satisfy the keenest student of tactics and courage.

Some good battle histories are crackling accounts of tactical moves and soldiers’ memories, stepping along as jauntily as a Sousa march. This one proceeds more like a stately symphony, solemn but enlivened by surprise digressions and meditations, taking its time, building to a finish that is familiar to all, yet seldom conducted so eloquently.

Ernest B. Furgurson is the author of “Chancellorsville 1863,” “Not War But Murder: Cold Harbor 1864” and other books of military and political history.


The Last Invasion

By Allen C. Guelzo

Knopf. 652 pp. $35